Webb Society Deep-Sky Observers Handbook: Open and Globular Clusters

Webb Society Deep-Sky Observer's Handbook Volume 3 Open and Globular Clusters .

Compiled by the Webb Society Editor: Kenneth Glyn lones, F.R.A.S. Written and Illustrated by Edmund S. Barker, F.R.A.S. With a foreword by Professor Helen Sawyer Hogg (David Dunlap Observatory, University of Toronto)

Enslow Publishers

Hillside, New lersey 072 05

1980

To Professor Helen Sawyer Hogg, Pre-eminent observer of Star Clusters, With gratitude and affection

Copyright

©

1980 by the Webb Society

All rights reserved. No part of this book may be reproduced by any means without the written permission of the publisher.

Library of Congress Cataioging in Publication Data Webb Society.

Webb Society deep-sky observer's handbook. First published in 1975- under title: The Webb Society observers handbook. Includes bibliographies. CONTENTS: v. 1. Double Stars.- v. 2. Planetary and gaseous nebulae.- v. 3. Open and Globular Clusters. 1. AstronomY-Observers' manuals. I. lones, Kenneth Glyn. II. Title. QB64.w35 1979

523

78-31260

In the U.S.A.: ISBN 0-89490-034-X (vol.3)

Manufactured in the United States of America 10 9 8 7 6

CON T ENTS l lu s trations Li s t O f I Fo r eword eface to the Handboo k Gen e r a1 Pr Vo l ume 3: Open and Glo bular Clusters p re fac,e to Open and Globul ar Clus ters In tro duct ion to

vi vii vi i i ix 1

PART ONE: Open Clusters Hi s t or i cal Revi ew 1. O_Ass oci ati o ns 2. G alac tic Open Clusters 3 . Catal o gues o f Open Cluster s 4 . Obs ervati on o f Open Clus ters

3 5 7 17 19

PART TWO: Globular Clus t er s Historical Revi ew 5. Gal actic Globular Clusters 6. Globul ar Clusters in External Gal axi e s 7. Catal o gues of Globular C lu s t ers 8. Observati on o f Globular Clu s ters

25 27 33 35 37

PART THREE A Catalogue o f Open Clusters Li st of Additional Obj ec t s

43 1 45

PART FOUR A Catalogue of Gl obul ar Clusters List of Additi onal Obj ects

1 51 1 89

APPENDI CES Clas s 7 Open Clus ters Furth er Observ at i ons o f Open Cluste rs The Di stance s of Clus ters Pho togr aphic Sourc e s for Open and Globular Cluster s 5 . Bi bl i ography

1. 2. 3. 4.

vii

191 1 97 201 203 205

FOREWORD

LIST OF ILLUSTRATIONS O-B2 A s s o c i ations within 1000 pc o f the Sun Di stri bution on the Gal acti c Pl ane oL 8. 1 Open Clusters Lumino s i ty Function of Open. Clusters and Fi eld Stars Colour-Magnitu de Di agram for the Ple i ades Colour-Magni tude Di agram for M67 Positions of 2 Flare stars in the Ple i ades Galacti c Di stributi on o f 1 29 Glo bular Clusters Colour-Magnitude Di agram for M 15 Di s tributi on o f Globul ar Clusters in NGC 42 1 6 star Di s tributi on i n the Globular Cluster Palomar 4 Bri . Fi eld drawings o f 1 7 6 Open Clu s ters wi ll be found between page s 48 and 1 35, and a further s ample o f 6· Open Clus ters o n page s 1 98 and 1 99 . Fi eld Drawings o f 5 3 Globular Clu s t. found be tween page s 1 56 and 1 8 3 .

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9 12 13 14 24 29 30 33 42 42

of the sky regard star c lusters as the mo st Som e watch ers 'ful ob j ec ts in the heaven s . Several mi l l eni a ago the open beaut1 e Pl ei ade s , s o c aught the imagination o f s ome early clU S t er , th they regulated their year by its heliac al ri sing. peo p l es th at thei r beauty when he wrote that the Pl eiad es Te nnys on captured tarS "Gl i tter l i ke a swarm o f firefl i e s tangl ed in a si lver s

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catchi ng young and profligate blue-white stars a;re braid". Eyeo f many open c lusters , s ome o f whi ch have red stars a fe atu re

to o . Only afte r the development of tel e scopes did globul ar clus ters light . c ome to be noti c ed with their hundreds o f pinpoints o fghtest. stars in Their import ance was recognized as ear1y as 1 7 1 4 when Halley shre wdly sugge sted that the luminous spo t s , inc luding the globular cluster l ater numbered 1 3 by Me s si er , "cannot fai l t o occupy Spac e s immens ely great" . Though globular c lusters are the olde st obj ects in the sky , they are by no means stati c , as Auwers ,

Luther and Pogson l e arned in 1 860 when they s aw Me s s i er 8 0 in Scorpius change its appearance with a s eventh magnitude nova in its core . When and where wi l l the next such nova b e s een in a globular cluster? Frequently change can be no ticed in the c lusters numbered 2 , 3 and 5 by Me s si er when one of their bri ghtest stars bright ens an d fad es as a peri odi c vari ab l e . It i s smal l wonder that s ky watchers wi th telescope s , or even just binoculars , are eager to obs erve s t ar c lusters . Thi s volume is a conven i ent pathway and guide to such obs ervat i ons . For a century great encouragement has been given to sky ob s ervers , first by the Rev . T . W . Webb and l ater by the Soci ety founded in hi s honour . My sincere congratul ati ons go to the Webb Soc i e ty and its editor Kenneth Glyn Jones for producing thi s Handbook on Star Clu s te rs as Vo lu me 3 of the Webb Soci ety Deep-Sky Observer' s Handboo k . H e l en Sawyer Hogg

viii

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General Preface er the Rev. T.W. Webb (1807-1885), an eminent amateur Named aft and author of the classic Celestial Objects for Common a stronomer the Webb Society exists to encourage the study of double stars �lescop�k, objects. It has members in almost every country where amateur deep s y and flourishes. It has a number of sections, each under a director a�tro�� experience in the particular field, the main ones being double w1th lae and clusters, minor planets, sttpernova watch and astrobu stars, n . publications include a Quarterly Journal containing articles photOgr hY ial features, book reviews and section reports that cover the and s , s activities. Membership is open to anyone whose interests are socie are available from tible. Application forms and answers to queries 1 Cramhurst Lane, "Chestnuts", Society, Webb tary, Secre ton, .S. Whis England. rey, Sur Witley,

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Webb's Celestial Objects for Common Telescopes, first published in 1859 must have been among the most popular books of its kind ever writ en. Running through six editions by 1917, .it still is in print although the text is of more historical than practical interest to the amateur of today. Not only has knowledge of the universe been transformed totally by modern developments, but the present generation of amateur as tronomers has telescopes and other equipment that even the professional of Webb's day would have envied.

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The aim of the new Webb Society Deep-Sky Observer's Handbook is to provide a series of observer's manuals that do justice to the equipment that is available today and to cover fields that have not been adequately covered by other organisations of amateurs. We have endeavoured to make these gu ides the best of their kind: they are written by experts, some of them professional astronomers, who have had considerable practical exper­ ience with the problems and pleasures of the amateur astronomer. The manuals can be used profitably by the beginner, who will find much to stimulate his enthusiasm and imagination. However, they are designed primarily for the more experienced amateur who seeks greater scope for the the exercise of his skills. Each handbook is complete with respect to its subject. The reader is given an ade quate historical and theoretical basis for a modern under­ ing ?f the physical role of the objects covered in the wider context e un verse. He is provided with a thorough exposition of observing � m th O s h s mlcrometers and simple spectroscopes. Each volume contains a . de a �ed and comprehensive catalogue of objects for the amateur to locate and observe with an eye made more perceptive by the knowledge he has O gained

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ope that these volumes will enable the reader to extend his ab i t e l �, to exploit his telescope to its limit, and to tackle the cha lle n succes glng difficulties of new fields of observation with confidence of s. xi

Prefac e Volume 3: Open and Globular Clusters of c eles ti al obj e c t s covered in thi s volume can both Th e t wo kOnds as s t ar-clus ters . However , in astronomical terms bed cri d be l o o � elYer : all respec t s . Open clusters are young in the st almo �n th e y d: ff mo s t o f them are c omparatively near to us in and e scal evolut � on a:Y the globular clu s t er s on the o ther hand have hi s tori e s our G al Y · to the very beginnings o f galaxy-formation , and some of th at go aC k di s tant that they may be vi rtually free o f the gravi tati onal th e m ar e so e Gal axy . fi eld of th the amat eur observer they pre s ent no t only very di fferent vi sual bu t also require very di fferent methods o f observation. The as pe c to s eparate from the bac kground � ste rs may o ften be di ffi culte asy o pen to r e solve: in drawing at the generally are they but _ d iel ' t r however , great skill and pati ence are required to produc e an e s cope usually conspi cuous in are s er t s clu Globular . on entati ; s epre aC rat e for a large number o f them , the resolution into but ance , ar e nsti tuen t star s may t ax the observer ' s vi sual' acui ty to the utmo st . The imaginati on may well be s ti rred by the s i ght of one of the ' great ' globular clusters - such as omega Centauri or M 1 3 - in all the glory of i t s myri ad s t ars: the open clusters have a more ae s thetic appeal , and not even the fines t as tronomi c al pho tograph c an do justi c e to the pri smatic beauty o f the double-cluster in Perseus ( h and chi Persei ) or the ' J ewel Box' in Crux as s een in even the m o s t mode st o f amateur telescopes . Thi s volume provides a more than ade quate hi s tori c al and theoretical background for the reader to appre c i at e the importanc e o f both clas s e s o f star-clus ters i n their di fferent astronomic al aspects . Expert guidan ce is given in the selection, location and clas si fi c ation of objec ts in each fi eld , and as in e arlier volumes , useful hints are provided on observing t echnique and recording. In addi tion a selected cat alogu e in each clas s , c omplete wi th �umerous fi eld drawings , has been compiled from observations mad e by members of the Webb Soci e ty over the year s . Observers will find thi s an invaluable ai d to rec ogniti on for many o f t h e more ' di fficult ' o b j e c t s , and a useful mp ari s on for their own o b servations . Altoge the r , some 205 open us � er s ( 1 7 6 o f them wi th drawings ) and 6 3 globular clu s t ers (53 wi th raW1ng s ) are included . Almo st the EdmUOd Bar er whole of the text has been wri tten in thi s instance by � , who as Director of the Nebulae and Clu s t er s Section, h as C -o r d1nated the many deep- sky observing schem e s undertaken world­ Wi d Y memb ers o f the Webb Soci e ty . In addi tion, Ed Barker ' S skill as d augh t sman i s mani fes t throughout the whole o f thi s volume: we are i n e ed for tunate that such talent s are given so uns tintingly . gr a t W th all our productions , the Edi tor wi she s to acknowledge wi th u e the con tri buti on of our Publi cati ons Offi c er , Eddi e Moore ,

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who has kept a watchful and expert eye on all s t age s o f preparati o n o f thi s volume . We extend our thanks als o to Ri dley M. Enslow J r . , Presi dent o f Enslow Publi shers , for hi s enthusi asti c support in our publi shing activi ti e s , and especially for hi s gui danc e and experti se in the reproduc tion of the all-important fi eld drawings in thi s and previ ous volume s . Finally , we wi sh to expr e s s to Profe s sor Helen Sawyer Hogg our deep grati tude for doing us the si gnal honour o f acc epting the dedi c at ion o f thi s volum e , and for so generously contri buting a foreward . Her eminence in as tronomy , especi ally in the fi eld of globular cluster obs ervation and analyti c al res earch , i s internat ionali acknowledge d , as i s her abi ding intere s t in and encouragement of many; the activi t i e s o f amateur as tronomers .

xiv

GENERAL

INTRODUCTION.

1

of information can be to which the maximum amounta direct The derrr eme any consequence of is study under ct obje ined i r s and method used, and nowhere is this more so than obtama the tef�e�d of observational astronomy . Often , however , the method n the ian be in advance of the means , and the time comes when c beiesee�n tovisual observation have virtually exhausted the abili:i � of a given telescope . It is at this point that financial pote�iO:S ari se; greater light-�athering q�alities demand a larger ue this in turn requlres a conslderable cash outlay. aqpers ture,ereand -lnches nces between telescopes 0f , for examp I e , 8 and 1 6· The diff view of of point the performance from both ble, sizea aP:rturecosare t. If we take galaxies as a class of object for visual of has access to a 1 6-inch would willingly o�: ervation, nouseoneofwho 8-inch. Bearing this in mind , it is an the to urn that deep-sky objects do exist in realizing ile worthwh fore ere �: a high percentage of information can be obtained with the which , and most of the trumentation ins inexpensive ely relativ of use present volume is concerned with such objects . In the field of visual observation of star clusters , the observer is confronted with objects that , in a large number of cases, exhibit a considerable amount of detail . Even quite small telescopes are oapable of fully resolving numbers of open clusters , while many globular clusters will allow at least peripheral resolution to be obtained, and in a number of cases total resolution is the order. With such morphology being relatively easy to determine , s tar olusters may legitimately be said to outrank other deep-sky objects in the context of resolution of constituent parts . Unlike many nebulae and , open and globular clusters are (with inevitable exceptions)galaxies not objects that present extreme problems in locating. Indeed, many examples abound where visual observation will reveal an object that can well-nigh dominate its ticular field , whereas a photograph of the region with i�esc a ope increases field s tar distribution to such an extentlarge that � t e cluster merge s to a large degree with the field. ver the whole sky a large number of clusters is shown on the At l � Coeli ts , and a selection of objects not plotted in Coeli is o�� of thechar aims of the present volume. A number of such clusters a h e served , and appear in the catalogue sections while a selec t�oen ob We hav enndof others will be found in the list of additional objects. ea�oured to achieve an adequate balance between the more we l l_ � wn ob les ser_�o Ject s that many observers are aquainted with , and wn but often equally interesting clusters. Ob server s lnv . ticular t p ariably find themselves gravitating towards a P� th e � e of object upon which they spend the greater part of opeinrColub:�rvlng time. This is illustrated in this volume, where the OQncen trateerds are primarily the province of a few observers who have to a large degree upon these objects. Interest and V

2

General Introdu ction. determination can produce qualitative comprehensive resul in observational astronomy , and hopefuland ly the results set out tsi n the present catalogues will act as a catalys t for those not Ye t aware of the variety of objects within a single , as well as showing how much can be achieved with moderateclass telescopes . Acknowledgements . David Allen contributed to the Appendix on cluster distanc es as well as contributing many observations to the es . David Pike and John Alexander of the Royal Greenwicatalogu ch Observa tory kindly supplied data on globular clusters and stellar associatio while further data on open clusters was supplied by Guy Hurst. ns Much of the research for this volume was undertaken at the libr ary of the Royal Astronomical Society and at Universi ty College 10nd on, The writer expresse s his thanks to the 1everhulme Research rds Committee for a research grant to aid in the compilation ofAwa this Handbook.

I

PART ONE : OPEN CLUSTERS. SISTeR!

3

CAL REVIEW. associated in cluster-like forms was noted o.e s !�: t �:omers !bateasrli : the Hyades and Pleiades (both true es by t he always been recognised as distinct have , e 1 p s ) for examthe grouping of the conste11a t·10n Taurus. clusteirsms larger wi thin however , defied resolution by Pleiades asterters sma ller than the and the, few Clus 1y unai that were observed before , ight eyes d de optical . on of under the vague classed all were telescope the the invetnhn f ' ebulae' (little clouds) or 'nebulosae' (cloudy d escri f O t � lem� listed seven of these, but only four, the double ( stars ) ) Ppers eus (h and� Persei) , Praesepe in Can�er, M7 in in clust �� and the 'cloudy convolution s' of Coma Beren1ces are true Scorp clusters , the other three being small asterisms. mer , Al Sufi, who , in about AD 954 , was the Tbe Persian astrono Nebula , also li�ted of the Andromeda existence the t or rep to . first asterism whi c h the 11ttle the 'nebulae' of ptolemy and added includes 4 and 5 Vulpeculae, and which has become well-known as 'Briochi's' cluster. He also included the star cluster . around kinds omicron Velorum (le 239 1 ). Other false clusters of var10US were added in the star catalogues of Ulugh Begh and Tycho Brahe, but with the advent of the telescope in the hands of Galileo , we first arrive at the recognition that 'the nebula called Praesepe is not one star only but a mass of more than forty small stars'. Galileo thought that all nebulae could be resolved into component stars, and this impression was to persist for several centuries. As telescopes improved in light-grasp and resolution , many new and diverse nebulous objects were discovered , including the open clusters Ma (Flamsteed in 1 680) , M1 1 (Kirch , 168 1 ) , NGC 2244 and M41 (Flamsteed , 1690 and 1702), M50 (Cassini, 1 711 ) . In the years 1745-4 6 the French astronomer de Chesaux discovered M6 , lC 4665 , Bce 6633 , M1 6 , M25, M35, and made a more-or-less successful attempt to differentiate between nebulae which were composed of stars and se 'rightly-styled nebulae which when seen in th. largest teltho esc opes, never appear as anything but white clouds. Two of the well-known open clusters in Auriga, M36 and M38 , �ere diScovered and demons trated to consist only of stars by Le n til 1 7 49 , (M37 was found by Messier in 1 764). In 1 751-52 t� e Abbein1ac aille , his expedition to the Cape of Good Hope, :��Piled a list of in 42 nebulous objects of the southern skies , h i some 16 new , genuine open clusters. 1acaille also atu: tCmptendcluaded fo d , di more rigorous classification of the 'nebulae' he had id g them into Class I - nebulae without stars; Class 11 ebulVouin s star by - n clusters and Class III - stars accompanied glo�:�Ulosity. Thi ss in scheme did in fact give a rough separation of clUst ers , open clusters nebulae, but the d1st1nar c tion was not entirely sharpandnordiffuse consistent enough to be

4

5 Historical Review.

1 . 0-ASSOCIATIONS.

meaningful at the time.

Neither Charles Messier, nor his imitator in the compilat ion Of catalogues of nebulae, J.E. Bode, made any attempt to classif y th e nebulae they listed, but the former gathered in his fruitful net a dozen new open clusters, although one of the finest of these M6 7 in Cancer, was first discovered by J.G. Koehler at Dresden 177 i

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It was, of course, Wm. Herschel who made the great leap for ward both in the discovery of new nebulae and in a more rigorous clasS' ification of them. His eight categories, from I ( bright nebula e to VIII coarsely scattered clusters begin to show divisions whi ch are meaningful, and although he did not include a separate class for globular clusters, he used the term as a description of many objects we now know to be of that class. The open or galactic clusters, as might be expected, are found among those objects he classified in the categories VI very compressed and rich Clusters VII compressed clusters of small and large stars and VIII coarsely scattered clusters .

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However, even Herschel's catalogues, and their successor, the NGC, did not always succeed in giving a clear separation between open and globular clusters. Even now, we know several objects such as the well-known M71 in Sagitta - so indeterminate in form that the distinction is difficult to apply, at least purely on morphological grounds. _

It was the recognition by WaIter Baade in 1944 of the existenc e of two separate populations of stars in our Galaxy the young Population I stars of the disc and the older Population 11 stars of the halo which served to distinguish more clearly the differences between the open and globular clusters.

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b inappropri ate to commence a survey o f the vari ous It WOUldrt a��ni ng to open clusters without first consi dering tho s e pe faotor s gr oupS known as O-as sociati ons and their relation to open ar l l s te m se two type s o f star group s are s�m� 1 ar �n many ways , olus ter s . 1 h ases are found to be c l o s ely linke d . and in s om e " stincti on betwe en 0-as so c1at1ons and open .T o de f":- ne a tru e di if we must pinpoint a di fference it would easy: olust ers � s not diameter , which , for the as soci ations , i s linear f o b e that hav� 1 00 pc. . The lower limi t o f linear s i ze f o order the f o tYP�·c lY em to be about 30 p c , and we c an compare e s would i ons for a- as so ci at lowe r limit for open clu sters , wh"�ch h overs aroun d a th the . w�. th�S diameters o f as sociations are , howeve r , qui t.e fi gur e o �so 1 pc . The ne ; mem b ersh1p S'" " � e ior any · " sl " t r1nS1C " and h enc e 1n di ffi cul t to determi many problems , and thus the membersh1p aspect posing st ell ar group can be s e en to parallel that of open clusters . f a_a sso ciatio ns en for the smaller as sociations r . is di ffi cult , but at least in such cas e s the boundari e s are fairly well -defin ed, whi l e with increasing si ze they become considerably more vague . As i s the c ase with open clusters , O-as so c i ati ons are unstable groups , and under the rel entle s s shearing e ffects of gal acti c rotati on they wi ll eventually di sperse into the surrounding star fields . Nany as sociati ons show an extreme overall ellipticity whi l e others di splay n o tendency towards e longati on i n the gal acti c plane, and thi s furni she s us with a c lue regarding the age s of as sociati ons . Tho se stars in an as sociation which are clo ser to the gal acti c centre move at a greater speed than tho se which are more di stant, and as a consequenoe o f thi s an as soci ati on wil l gradually spread out around the centre o f the Galaxy . Theory shows that , by thi s acti on, an as so ciation wil1 undergo a doubling o f its l ength on a time scal e of about 30 :le 1 0 6 yr . For as sociati ons younger than thi s , their resp ect ive expan sion velociti e s wi l l mask the elongation pro c e s s . A� the upp er end o f the age scal e , where we are c'o nc erned wi th lm e s OVe r twice that o f the above , the pro c e s s o f di s s o luti on wi ll e. wel l adv anced . exampl , di splays a 6 q�te pronoun ced The Sco-Cen as sociati on , for o f an e age of 70 x 1 0 elongati on whi ch i s indi c ative contr ast , the as soci ation around zeta Per , covering an area 1n the sky , i s a much younger group , with an age o f only about 1 0 Yr . T S CO-Cen as sociation contains the well-known dark clouds near rh o and al so contains a number o f sub-groups . Other associati ons also b and G r o � the latt , e n N 7 6 are q ? 1 0 re si. d e . Connecti ons between clusters and associati ons Ult e common , and i n the present catalogue c lu sters l inked with

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O-Associati ons .

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O-assoc i ati ons wi l l b e referr ed t o i n the data secti ons prec e din�c the visual o bserva ti ons . Finall y we must consid er the questi on o f ini t i al i denti f . o f an O-assoc i at i o n . This is made by determin ing a regi on i c atl On whe r e the densi ty o f stars o f types O-B2 shows a larger -thanmean fi e l d densi ty than i s acc ep tabl e as a chance arrang ement . Where the c ase , fUrthe r work i .8 necess ary i n order to obtain datathi s . m embership . An O-asso c i at i on wi l l give a fairly wel l-defi n on c o lour-m agni tude di agram as l ong as i ts back-t o-fron t rat i ed t o o great ( fo r ful l detai ls o f colour -magni tude di agrams o i s n 0 t see Chapte r 2 ) . Distan ces t o ass o c i at ions c an be estima ted from th e proper moti ons o f the const i tuent stars , the distan ce o f Sco-C en assoc i at i on being about 1 7 0 pc . In Fi gure 1 below the is pro j ec ted on t o the galact ic plane , O-B2 associ ati ons wi thin sh own, a distan ce o f 1 000 pc o f the Sun .

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OMon OB1 z = +27

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DUCTION.

purpose , namely t? of s t ar cluste rs have a twofold of their evolutl on , stud i e s ull anding underst an ble ossi p y as f s a n overal l struc ture the i to this a and to relate o bt t and fu ture , Galaxy . Both observa ti onal and theore t·lca 1 bo th pasut . n of the ft�d e.vol lO. chapter we shall .... re d'In this c ontext , and in this qul e . wor k'ln th e f'le Id 0 f . de r the various aspects o f thlS d at a lS r nsl co bri e fl Y ste rs . u cl n e p o . . . ; is divi de d into five secti ons: 1 . Classlflc atlon Th e cha te r the Galaxy ; 3 . Cluster morphology; 4. Ste � lar to . 2. Rel ati o d 5 Col our-Magni tude di agrams . These sectlons glve an ns ati � po pul ons moti stellar as a func tion o f . f0 rmatlon. on c l �ster li fetimes In , the re 1 a t·lon 0 f c Ius t ers derlvatlons age , tation ro c actl an d gal . .. clus t er s t ars lndlvldual , Galaxy the f o re tu struc . t o th� sP iral c luster reddening. The l atter has a bearlng upon ll na d i Y an ' ! ll wi be ch whi , on i derivat distance of on t questi the imP or tan 3. Appendix in lusters c ar globul and open both for d ere consi d

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Ori OB1 z = - 1 30

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INTRO

GALACTIC OPEN CLUSTERS.

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Lac OB 1 z = -1 65

Cep OB3 z = +37

Cep OB2 = +72

z

Sco - Cen 500 pc

Classi fic ati on . The classi fication of open c lusters wi th whi ch the. maj ori ty of the amateurs wi ll be fami l i ar is that o f Shapley , who devlsed following scheme: ( c ) very l o ose and i rregular ; ( d) loose and poor; ( e) intermedi ate rich ; ( f ) fairly ri ch; ( g) consi � erably . of baslc rich and concentrate d . This gives a good outllne cluster morphology, but is now superseded by a cl assi fi cati on scheme which ori ginated wi th Trumpler and which . be � i des givi � g a bri ef description of cluster struc ture , also furnlshes detalls on stellar membershi p . De tai ls of this classi fi cati on are shown below. Detached wi th strong c entral c oncentration. Detached wi th li ttle c entral conc entrati on . III Detached wi th no c entral concentration. IV No t wel l detached but apparently l i ke a strong fi eld c oncentrati on . The se Roman numerals are foll owed by Arabi c numerals , whi ch Used to con inform at i on on the luminosi ty func tion of the lg te st starsvey ( for on luminosi ty functi ons see section 3 inally , lett ers details are used to deno te the number of stars . p po or , less than 50 stars . m medium ri ch , 50 - 1 00 stars . r ri ch , over 100 stars . Th�s to tak e the cluster NGC 687 1 as an example , the Trumpler � cl is IV 3 p. This parti cular scheme is used in the o Randbo ogu e o f op en c lusters to be found in Part Three of this cIUs t k . In s� c ti on. 3 we shall c onsi der the morphology of open fUr th er , and in parti cul ar i t s rel ation to field star Ut i on and the questi on of cluster recogni t i on . I

11

�r7 � J •

Fi gure 1 . Posi ti ons o f O-B2 assoc­ i at i ons wi thin 1 000 pc o f the Sun . above ( + ) and Z = distances in pc below ( -) the galac tic pl ane .

ca�=�lflcation

d1.tr��s

7

8

Galactic Open Clusters.

Galactic Open Clusters.

Relation to the Galaxy. Open clusters are to be found inhabiting two population group in the Galaxy; young clusters , along with 0 and E stars , occ ur isn the extreme Population I regions , older clusters in intermediat Population I. Stellar populations will be discussed in section 4e and we shall therefore, in this section , consider the role of open clusters in defining spiral structure and also the association of clusters and nebulosity. The spatial distribution of open clusters varies as a func tion of galactic latitude, and this can only be ascertained by obtaining distance determinations that are as accurate as possible. Onc e the cluster distances have been derived , then it is possible to arrive at figures showing their distances perpendicular to the galactic plane. These, as we have seen in Figure 1, with regard to stel lar associations , are defined by the letter which denotes these distances in pc. In star atlases , such as Atlas Coeli , the maj ority of open clusters appear within the confines of the Milky Way i80photes . This , however, gives us no indication of their distribu tion in nor does it show how clusters can aid in defining the spiral s tructure of the Galaxy, as the great circle of the Milky Way , seen with the eye, is comprised of different spiral arms. In some cases , e.g. , Cygnus , we are looking along a spiral arm , while in others , e.g. , Auriga, our viewpoint is essentially at right angles, Nearby clusters such as the Hyades and Pleiades appear to the eye as being outside the apparent boundaries of the galactic . plan e , This is purely a result of their small distances from the solar system , and the further we see the more clusters will appear to be located within the Milky Way confines. Nevertheless , the Hyades are at a fair distance from the galactic plane, with -23, wh ile another naked-eye cluster , Mel 111, better known , perhaps , as t h e Coma star cluster , has +85. As we approach the plane of the galaxy the space density of open clusters increases , and this is a suitable point to discuss clusters as delineators of spiral structure. In Figure 2 overleaf the distribution of 81 clusters is shown projected on to the galactic plane. The circle enclosing a dot defining the position of the sun. The delineation of section s of three spiral arms is easily apparent , the section at the upper right being the Perseus arm , the central section , including the�, US sun , the Carina - Cygnus arm and the lower section the Sagittar arm. A further correlation can be made by plotting H 11 regions, H I regions and stellar associations on to such a diagram. These too will be found to be indicators of spiral structure, and occupY similar positions to those of the open clusters.

9

2.

I

0 0

, " ." 0

z,

o

, ,',

'

',' .

.

o

•

0

.

.

. , .

" o

00

0 ,

:

.

,

'

o

•

, "

0

0

z,

z

z

=

=

1

kpc Figure 2 . Distribution on the galactic plane of 81 open clusters , showing the delineation of three spiral arms.

On the eding page we have mentioned how H 11 regions can be fit ted to prec the plotting shown in Figure 2 . It will thus be obvious that incluster many cases associations of clusters and nebulosity occur , and we shall briefly discuss such amalgams below. ObVious associations of nebulosity and clusters are objects :uCh as MS (comprising the cluster NGC 6530 and the bright and ta8r: nebulosity catalogued as NGC 6523) and M16. A further example al tho h here the cluster aspect is not as obvious as in prev4i2, ous two ug cas es . i mp o rtant effeot of dark nebulosi ty is its ability to dim 8ta� r an d c lusters associated with nebulosity will often be qUitaight, h e a V i 18 a e ly reddened by obscuring material. This dark nebulosity when seen in oonjunction with regions of brigh t nebuIPar aa , nast einsoutgh he case with M8 , but often no bright matter is '.eQ � '� J,� d i s uoh n cases where a cluster is affected by interstel lar , Pho tome try can supply details of the dimming. The young

10 Galactic Open Clusters. cluster lC 348 lies within a region of dark material which Cont at least one heavily obscured luminous star , and it is thereforeaine highly likely that the visible part of lC 348 is only a small par t of the total. Bearing in mind the patchy nature of the interstellar medium . is evident that the effects of this upon clusters will vary qUitelt considerably. Absorption figures range from as low as 0.15 mag NGC 6281 to over 1 2 mag for a recently discovered cluster. Furthfaer details of clusters and nebulosity will be found in Chapter 4, Wh�l below , in Table 1 , we show the diameters , in pc , of selected as soc�e iations of clusters and nebulosity.

Galactic Open Clusters. a:n

11

personal designation s. These asterisms d even given tive fields in much the same way as respec r ll in thei , and a few are to s edgenUl :: open clu sters of sparse membership as bona-fide ly plotted erroneous , Atlas som und in Norton' s star b e fo clu s ter s cal parameters of a cluster are useful ; they define Theageeom�hterinumeric al richness of its stars and their density sh 'and thes e alone will be enough to differentiate an open igrts ie ad n�fro majority of globular clusters. Nevertheless , m the greatristics clust� r . of a cluster are also important , and racte cha the p ayS1ecal composition , age and luminosity chemical the by ined def thesc�i � of the cluster stars. To extend knowledge of a·cluster O photographic appearance, therefore , detailed photometry fun Table 1 . Clusters and Associated Nebulosity. b eyond its Diam. Neb·(Ec } Diam. C.(EC} Association. and spectros copy of t s s t ars are needed of astronomy , it is natural that the brighter , In all bran ches 25 18 NGC 1 893/IC 4 1 0 receive the maximum amount of attention. In the will cts obje a g l er r 15 8 2 1 75 objects such as those in the Messier cata­ clusters open of field 50 12 2244 and detailed observations go back for many , ed well-studi are gue lo 7 7 2264 large , bright clusters not in Messier have also been Other years. 1 50 4 2579 subjected to the full range of observational procedures , but we 14 14 651 4 (M20) still find that a large number of clusters are either only partially 40 21 6523/30 (M8) studied or not studied at all, apart from basic classification. In 30 6 this context it is worth recalling that the first photometric 661 1 (M1 6) observations of NGC 2420 did not take place until 1 962. As well as 90 12 IC 1 805 relatively little-studied clusters in the NGC , there are also many 30 14 1 848 more among the discoveries made by Ruprecht , Dolidze and others. 8 8 69 Cr Furthermore, with numbers of recently discovered clusters or 30 35 302 possible clusters cropping up in the southern sky , the situation is unlikely to change for some time, bearing in mind the great amount of work required in order to study a cluster fully. 3. Cluster Morphology. In this section we shall concentrate primarily upon the problems Lum�osity Function of Open Clusters. e � sity function of a cluster is obtained by counting that can be encountered in identifying open clusters . It may seem e n umino er of at first thought that nothing could be simpler than defining a:ny li th star s in each magnitude interval or step, and this � W fer from the luminosity function of a non-cluster field. open cluster; that any not-too-compres sed , globular-like object . eouol Inillthe Ifat case , the luminosity function is seen to increase be nothing but an open cluster, and vice versa. This , however , lthSen with de rete: the case, for it must be realised that morphology alone is no t fu ncti � � slns gamagnitude , while in the case of a true cluster the rise to the brighter cluster stars followed by a determining factor in cluster recognition. Many other factors aruSe tell decreaose �oowthe fainter one s. valid, not the least being the types of stars comprising any cl Figure 3 on page 1 2 shows the mean luminosity be it open or globular. o function of true ' pen l c us .e eld lstarters comp�red with the apparent luminosity function of In the past , difficulties have often been encoun.tered in �he f�1I11 fCilus �he dlfferences are immediately apparent ; the open of cluster classification , it being uncertain whether to ass1gnc tSt# th ters s��wlng e clusters to either the open or globular category. Examples of e 11 nitufield tar s dia mean maximum absolute magnitude of Mv =+5 while splay maximum numbers at fainter apparent mag­ des. H�w individual cases will be given in Chapter 7 , and therefore we sh� i l l a whil � ver, teS e the greater percentage of open clusters a � Sho 1 agglomer from clusters open true of now discuss the sifting w os ity function equivalent to Figure 3a , it is rue to s ay t�amin field star distribution. t not necessarily all will do so. � Lying among the rich star fields of the galactic plane, the:eg to be found groupings of stars which give the impres sion of belned coarse open clusters. Such s tellar concentrations are often logg �ate ur s, out. ta n

.

. 1

•

12

Galactic Open Clusters.

Galactic Open Clusters.

100 90 BO 70 60

N (Mv) ,.... l�

f-

-

,-

a.

f-f-I-

-

I

+2

I

I

T

h 1

Mv

-

+10

50 40 30 20 10

b. V

+B

+12 +16

Figure 3. a, Mean luminosity function of real physical clust er s selected by van den Bergh (1 961). b , Apparent luminosity func­ tion in the case of field stars. stellar Populations. In the historical review we have seen that the concept of stellu populations originated with Baade. Nowadays the scheme has been elaborated , and comprises five population divisions , as can be seen below in Table 2 .

4.

Table 2 . Stellar Population Group Extreme Pop. II Intermediate Pop. 11 Disc Population Intermediate Pop. I Extreme Pop. I

ColoUr-Magnitude Diagrams. evolutionary s tage and lity to cast light on the current of T � aabista unction great the is cluster r � . a colour-magnitude . o a� am T he use of such a d�agram �s not conf�ned to clusters dl agr however ; certain types of field s tars are also subjected to alucohn e�alysis , as well as luminous s tars in nearby galaxies . s to s tar fields within the Galaxy , when we look at I con tra st or a globular cluster we are seeing s tars which are open an e ith:prrox age and with the same initial chemical the ely imat of :p ition. A colour-same of a cluster is obtained by magnitude oom osing the brightne ss of as many of its stars as possible in sur visual (V) wavelengths and then plotting V agains t ��:e (B) and the latter defining the star's colour. If stars in an open j-V a well-defined locus is obtained , known as olu : ter are so plotted certain s tars will form a t he m ain- sequence. In some clusters giant the as branch; in very young known diagram the region of will be lacking while in old clusters it is more in this ters olus evidence. While, as described above, the apparent magnitudes of cluster stars can be plotted on to a colour-magnitude diagram, to obtain data on the ages of clusters their distances are required in order that the apparent magnitudes can be converted into absolute magnitudes (M ), which is the magnitude a s tar or any ot her object would dis play at a distance of 1 0 pc .

�

N(V)

I-

-

13

Populations in the Galaxy. % of Met al� Type of star 0.3 Halo globular clusters 1.0 RR Lyrae and halo s tars 2.0 Main-sequence stars 3. 0 Old open clusters 4.0 Young open clusters O-B stars.

From the above table it can be seen that there is a wide diSpetilr�l', sion in metal abundance as a function of galactic latitude , and will be further discussed in Chapter 5 with regard to globular clusters. As well as the metal-rich open clusters, Population I regions of the Galaxy also contain classical Cepheid stars. TheS eet variables are also to be found in some open clusters (e.g. , UY p and VY Per in the Perseus Double Cluster , USgr in M25) and are useful in deriving distances of the clusters in which they occur. Further details of this will be found in Appendix 3 .

M

v

-6 -4

Figure 4 . Colour-magnitude diagram for the Pleiades. The abscissa is the colour index (B-V), the ordinate is the absolute visual magnitude (Mv).

-2 o

+2 +4 +6

+0. 4 +O.B +1.2 +1.6 (B-V)

14

Galactic Open Clusters.

Galactic Open Clusters.

15

On the preceding page is shown a colour-magnitude diagram fo ges. The star, characterised by a larger angular size Pleiades. The band running from B-V + 1 . 2 to M -3 is the cll.' th, undergo ���ur, defined as a red giant, and many well-known stars s m�in-sequenc?; individually plotted cluster sta�s would basical� tel and r;d i type,ise.g., Antares, Aldebaran and Betelgeuse. th S 11e along th1s line. It will be noted that there is no red giantY are 0 from the above that the lower the turn-off point branch for this cluster, which is indicative of its young age. be seenquenc Itthoan e the older the cluster. It is apparent, there­ old open cluster M67 does, however, have a giant branch, as canThbee -se ain fro� e � Figures 4 and 5 that the pleiades is a young cluster and seen below in Figure 5. fore, �7°�s decidedly older in that it has a well-developed giant Mv that M further examples of well-known clusters, the Perseus b ranoeh·ClTwo and the Hyades, show this difference in a less extreme er ust DOubl the Pers -6 eus clusters the main-sequence is virtually intact, n i fo�; the Hyades has already lost its blue stars to the giant branch ..,hile of cluster ages also demands a good deal of theorderivationwhich -4 Th work observations can be compared. Theoretical with � of stars in a cluster in order Figure 5. Colour-magnitude e ti�a�odels can be fitted to a sample c e ' whil. ions, derivat �AM ge diagram for M67 . a in aid -2 from the ZAMS are also important. In the past, these t�a cks of stars nary tracks for stars often agreed poorly with evolutio ical ret theo in the form of a colour-magnitude diagram, plotted observed dataages derived o for clusters are well below these early t curren and deriv9tion of the age of the open figures; for example, an early cluster NGC 1 88 was about 1 4 - 1 6 x 1 0 yr, while a 9recent figure by +2 Hirshfeld, McClure and Twarog ( 1 97 8 ) gives 5 x 1 0 yr as an age for this cluster. At the other end 09 the scale there is the Hyades, to which age of only 0 . 7 x 1 0 yr has been assigned. For an even younger stellar group we can take the CMa R1 association, in which +4 a number of hot stars are to be found illuminating nebulosity. In this association, which includes the emission-line stars Z CMa and RD 53367, no stars later than B5 are on the main-seq�ence, leading ) yr. to a possible age for the group of only about 3 x 1 0 The derived age for the Pleiades is about 2 0 x 1 0 6 yr, but it is :� on of the youngest clusters, the Perseus Double Cluster and -0 . 4 0 . 0 + 0 . 4 +0 . 8 +1 . 2 +1 . 6 236 2 both being younger, the age of the latter being put at ab ut one (B-V) ntie�h �hat of the Pleiade�. Another yo�ng cluster is M39 Wh retwe the maJorl. ty of stars are st111 on the mal.n-sequence, and � a ew of the In stellar evolution, a proto-star will lie off to the right of just brightest are in the process of evolving towards the red g iant stage. the main-sequence. As the star evolves, it will eventually make contact with the main-sequence, the point where it does so being bu! further consideration regarding cluster ages is that of metal dependant upon its mass. A large mass star will make contact with a d ar ll the main-sequence at the upper left of the diagram, where ste ­ forme��� · aBeing r?latively you�g objects, open clusters were s�age l.n the evolut10n of the Galaxy when the inter­ luminosities are high, while a small mass star will join the main stella a l from which they coalesced was much richer than at sequence at the lower right, and will hence be an object of low t1'n! earlierr emapoter1 �hs , this being due to metal enrichment of the inter­ stella intrinsic luminosity. The locus of points at which stars of diffe r �ed1 um by successive generations of stars, each generation fO rm in masses begin life on the main-sequence is referred to as the Zer o Age Main Sequence (ZAMS). From then on the evolutionary track of a earlierg l.� ra more metal-rich environment due to mass loss from HoweYe S � s by Yarious means, including supernova explosions. star is determined by its mass, the larger mass, high luminosity r t ere is a significant spread in metal abundance in clusters Of a stars evolving more rapidly due to the high rate of their nuclear gi � l a t �, :� age, and hence interstellar material in the disc of the reactions. Although a star will spend the majority of its life ime : re clusters reside, has obviously been unevenly mixed i � n � on the main-sequence, it will eventually move off to the upper g Pa epochs of galactic evolution. Older open clusters such S right of the colour magnitude diagram as its nuclear reactions =

::

•

an

16

Galac t i c Open Clus ters .

3 . CATALOGUES O F . OPEN CLUSTERS .

as NGC 2 4 2 0 and NGC 2 506 show a degree o f me tal defi c i ency . Th e s e clusters , along wi th o thers , l i e in the regi on o f the gal ac t i c ant��t 1. c entre , and 2 t o 4 kpc from the gal ac ti c nuc leus . Data on m e t al defici ency for a l arge number of c lus ters now ind i c a t e s that wi th increasing di s t ance from the gal ac ti c c entre , c lus ters show a d ec 9 in m e t al abundanc e , and that for about the last 5 x 1 0 yr the p o �a1t of a c luster in the Gal axy d e t ermine s i t s me tal c onten t , and no t t !, e c lu s t e r age .

� �

Finally we c om e t o the the que s t i on o f the s tabi l i ty of open c lu s t ers , o r , t o put i t ano ther way , over what peri o d o f time is a c lu s t e r liab l e t o retain i t s i denti ty as a uni t? For a c lus t e r to be s t abl e , i t s int ernal gravi tation mus t exc eed the t i dal forc e s of th p arent gal axy , and t o do thi s i t mus t have a den s i ty greater than ae specific figure . We can arrive at thi s fi gure by mul t i plying the maaB o f the Gal axy by 1 0 and divi ding i t by the cube o f the di s t anc e be tween the two rel evant c entroids , that o f the Gal axy and that of th ' c lus t e r . From such c omputati on s i t c an be demons trat e d that all tho se 3 c lus ters whi ch have s t ar dens i ti e s l e s s than one s t ar per 1 0 pc are very uns t abl e , and wi l l therefore be qui ckly di srupted by gal actic ti dal orc e s . In the P l e i ade s , the c entral densi ty i s about 0 . 1 s t� 5 per pc , whi ch makes the s e regi ons fai rly s tabl e , although n o t by a l arge amoun t . The den s i ty o f s tars in the Hyades i s about one qu arter of the P l e i ad e s fi gure , and the degree o § instabili ty i s thus much gre ater . On a time scale of about 2 x 1 0 yr about half o f the origim s tars in a cluster wi l l have di spersed owing t o ti dal forc e s and the perturbati on s o f n e arby s t ars , and thi s add s further we i ght to our knowl edge that o p en c lus ters are young o b j ec t s . From thi s i t can be s e en that many c lus ters whi ch once exi s t e d have now bro ken up , and that their c on s ti tuent s t ars have di spersed wi thin the s t ar fi elds of the Gal axy .

17

clusters th �t the great maj ori ty o f amat eurs l i s t of ope� in the Atlas C o e l i c atal o gue , . l i ar wi th l S that contalned e the who l e sky . Two of the s e , over ers t s lu c 3 2 r f o s 4 l ai ram: det a ves 'tIhio h gl , NGC 6 5 58 and ar e erron eously c at al o gued gl obul ar c lus t ers 2 Fr om the point o f vi ew o f thi s vo0 lume , whi ch has ( wi th a bo we NGC n.s ) a declinati on l imi t of _ 3 0 , Coeli l i s t s 1 8 7 open � X c e tio f ew s gives a l arge and vari ed s ampl e , but by no means Thi e s lu S · th e numbe r o f c lu s t ers avai l ab l e t o the vi sual observer , � e xhau S s clu s t e r s being o f e qual or gre ater int ere s t than r the omi t ted m any ° Coeli chart s . the on ed ott tho s e pl eur re ference , i t i s ins truc t ive W . th coel i as the s t andard amat C o e l i open c lu s ters were t aken . the ch whi from our�e s the at k t l o c ompi l e d by Shap l ey in 1 9 3 0 , ers t s 2 clu f 9 o e 4 T i S i s the catal o gu i er l i s t s such a s that o f arl e on advance great a was t i nd whil e s e d as c omprehensive for the s a l c be t anno c t i ) ers t s clu 2 6 1 ( e el ott p%e sent day obs erveT . Sinc e Shap l ey ' s c at al o gue app e are d , many new clu ster s have been s i ft e d from the rich s t ar fi elds of the Gal axy , 'tIhi l e any e
66� : �

� :

�

Table 3. Bright Open Clusters Omi t t e d fro� C o e l i . NGC

1 36 225 381 1 444 1 778 2232 2251 2286

o r a comp rehens i ve c at al o gue o f al l re fF t o t e Cat logue of S t ar Clust ers , fi r � app ea P� b h s hed ln 1 9 58 , s e c ond edi tion r

NGC 2 3 3 1 2 3 43 2374 2395 2 3 96 6568 6 8 00 7082

typ e s o f c lu s t ers we mu s t A s s o c i ations and Group s , 1 97 0 . Nine suppl ement s e be twe en the two edi t i ons , in whi ch Helen Sawyer Hogg co l l ab ra SUP l te d wi th o ther c ompi l ers . The mat eri al contained in the se P e t � was inc orpo rat e d i n the 1 9 7 0 edi tion , whi l e more rec ent m at e r a i Wl ll appe ar in a thi rd edi ti o n . Thi s c at5 a1 o gue c ompri s e s dat.a and referenc e s for 1 0 3 9 open c,lu s t e r s mo ving c lu s t ers and 1 1 s t ar group s , the information bei ng p r ' e o n 7 0 a o S n t e d on 1 1 8 5 c ards . Al so i nc luded are 8 6 c ards wi th data s SOc · a l t i o ns plus fur ther c ards on gl obular c lus t ers . O r th e 1 0 3 9 open c lu s t e r s in thi s pub l i c at i o n , over 700 are no t

�

:�

�

�n

18

C at.al o gu e s o f Open C lus ters

4 . OBSERVATION OF OPEN CLU STERS .

or IC o b j e c t s , and of the s e only 2 7 are to be found in C o e li . h l e av e s a l arge r e s i due whi ch c an b e frui tfully employed by the arnaTt I and whi l e many o f the s e c lu s ters are not p articularly interes t i ng , � vi sual s ens e , many wi l l be found t o b e chal l enging o b j ec t s for theIn maj ori ty of amateur t e l e s c op e s . A few o f the s e c lu s ters , o b s e rv e d ' a 1 0-inch t e l e s c op e , appe ar in the c at al o gue in P ar t 2 o f thi s V0 1 ( whi l e a s e l e c ti on o f o thers i s given in the l i s t o f addi tion al o b ' ! J eel The number o f known c lus ters has inc reased considerably since Hel Sawyer H o gg c ompi l e d a li s t of over 500 in 1 9 5 9 . Currently many n ewl� di s c overed pro bab l e groups are emerging from surveys in the sou thern)' hemi sphere . Some o f the s e app e ar very l i ke as t eri sm s , being of sp �s member ship and l o o s e struc ture , and only de tai l ed s tudy wi l l even tua;' d i s c l o s e the ir true nature . The fol lowing re ferenc e s give details ot : ' f e w o f t�e s e more recen t di s c overi e s .

NGC

�

Loden, L . O . Moffat , A . F. J . Vo gt , N .

Van den Bergh , S . Loden , L . O .

1 9 7 3 , Astron . & Astrophys . Supp . 1 0 , 1 2 5-1 3 3 . ( 44 clus ters in the C ar-Cen regi ons ) . 1 97 5 , As tron . & As trophys . Supp . 2 0 , 8 5- 1 5 3 . ( 1 1 previ ously uncatalogued C lusters ) .

1 97 5 , As tron . J . 8 0 , 1 1 - 1 6 . ( 6 3 unc atalogued Clust ers ) .

1 97 9 , As tron . & Astrophys . Supp . 3 6 , 8 3-9 3 . ( L o o s e c lu s t ers in the S . Mi lky Way ) .

19

RO DU C IN T

TION .

. . der ation i s t aken of the w�de d� spers � on �n angular . i s n o c Vh en bY open c lus ters , p lus their vari ed morphol o gy and range s sh elescopes size l e s t ar s , i t c an be s e en that all s i z e s of t b s er of o by teurs as we l l as binoculars , are catered for . A number of u sed l e s s ; r s i z e and bri ghtn e s s than the P l e i ade s , Hyad e s , M44 c lu s t e rsp � rs eus Double Cluster can be naked-eye ob� e c t s in a go o d � ky , th�i and cul ars wi l l increase the number sub s t an t � al ly , al though �n i �b l e i n s �� c e s adequ ate resolution wi l l not be obtained . m any ju s t i c e to open c lu s t ers , l arge t e l e s c o p e s ( by amat eur T� d� full not required , an aperture of 8 to 1 0-inche s , in a go od ) are s t an �r s bein g perfe c tly sui t abl e . Certainly a t e l e s cope of e i ther n t ° lOC� e ' si z e s i s not only i d e al for s tudy o f a c onsi derable number s o � and IC clust ers , but i s al so useful for extending observations that are ei ther l i t t l e-known o r c omp l e tely unknown o include obj e c t s content s of the pre s en t catalogue wi l l show , t° many amat eurs . As the been suc c e s s fully observed wi th , a 1 0-inch have latter the of ber num ;efl ector , whi l e a further s e l e c t i on of such c lus ters wi l l be found in the list of addi t i onal o b j e c t s . The chapter i s divided into two s e c ti ons : 1 . I den t i fi c at i on o f open clusters and 2 . Cluster charac t eri s t i c s , the l atter including passage s on unresolved s t ars , as s o ci at e d nebul o s i ty and s t ar c o l ours . Details wi ll al s o be given on the two bri gh t e s t flare s t ars in the Pl eiade s , a c luster whi ch is ri ch in the s e o b j e c t s . .

.

�� am;

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1 . Identification o f Open Clust ers .

The problems inherent in c o rrect identifi c at i on o f many clusters ar e not only related to tho s e of smal l angular diam e t er and faint st ellar membershi p ; l arge , qui t e rich c lus t ers can also pre s en t identifi cation probl ems when they are as s o ciated wi th ri ch fields . Equally diffi cul t c an be c lu s t e r s of sparse membershi inhabi ting � s imi lar field s . Chance ali gnm en t s o f s t ars ( as t eri sms ) c an al so be mi sle ad ing, and , often lacking the faci l i t i e s to check resul t s i �� nst such pUblic ati ons as t h e P alomar Sky Survey or Vehrenberg ' s un as Ste llarum , the obs erver i s l eft t o make the b e s t he can o f c e rt ain Ob servations . ' R ef er en ce pho t o graphs o f c lu s t ers are a great as s e t ; unfortunat ely tho s h oto graph s that usual ly appear in books and j ournal s are inva� . P a t th� ab ly �f the bri ghter , we l l-known o b j e c t s , imp o s sible to mi s t ake be fou �y?p � e c e . In some cas e s pho tographs of o ther c lu s t ers are t o n �n p publ ic at i ons , rofe s s i onal j ournal s , and a l i s t of the s e , plus o ther wi l l be found in Appendi x Th e p 1 ob serV � om ar Sky Survey print s are very us e ful for che cking at profe s s 1 0 ns , . but not only are tho s e copi e s whi ch are housed in i l s an e onal 1 ns t i tutions unavai lable t o mo s t amateurs , their purchase a en h �e i s ive ( al though rewarding) busine s s . �he P al omar prints O lU a ta� mi ti ng magni tude o f over 2 0 mag , and large numbers o f open e s apP e ar prominen t ly . I n c ertain c as e s , howeve r , a c lu s t e r wi l l .

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Obs ervati on o f Open C lu s t ers .

21

O b s ervation of Open Clus ters .

l i e in a regi o n o f parti cularly ri ch s t ar di s tri bu t i on , or be he avi l swamped in emi s s i on nebul o s i ty , and in such cas e s i t i s o f t en di f fi cY t o define the c lu s t e r . A sui t able example i s Cr 42 8 ; vi sually th i s \lIt c lu s t er app e ars as a l o o s e ly-stru c tured obj e c t showing no grea t d e � o f s te l l ar concentrat i on . L o o s e as it i s , however , it does s t and Ou tee vi sually in a m oderate t e l e s cope . The same canno t be said of the ima €e o f thi s c lu s t e r on the Sky Survey . On the red ( E ) print Cr 428 i s t o tally swampe d by the great expan s e o f the North Ameri can Nebu la ""h' even on the blue (0) print , there i s no real indi cation o f a c lu s t er l: t o heavy contaminat i on by fi e l d s t ars . Numbers o f vi sually ob s erved dt s tars c an , however , be i denti fi e d .

I den t i c al i n many ways i s D o l 5 . Again f i e l d s t ars overpowe r the c lUs t e r , al though no t to such an extent as in the previous cas e . Some s t ar s obs erved vi sually can be i dent i fi ed , but on the Sky Survey print the fields t o the W o f Dol 5 are vi r tual ly o f equal den s i ty t o the c luster regi on . Furthermore , bri gh t and dark nebulo s i ty of qui te hi � int ens i ty cri s s-cro s s e s the c luster nei ghbourho od .

In many cas e s goo d corr e l ati oI]. c an be achi eved be twe en vi sual and pho t o graphi c app e aranc e . On the Sky Survey smal l , c ompre s s ed c lust ers such as Mark 50 pre sent pho t o graph i c image s that di ffer but li t U e frol the i r vi sual appe aranc e . Wi thout ci ting further examp l e s , i t can b e said that c ompari s ons o f thi s kind are very sati s fying, showing as the) do j u s t how much detai l can be re s o lved i n many c lu s t ers wi th telescop! o f m o derate aperture .

Due t o their proximi ty t o the s o l ar system , a few open c lu s t ers app, t o be si tuated well away from the boundari e s o f the galac t i c plane . Fo! northern hemi sphere o b s ervers the prime examp l e s are M44 , M 4 5 and the C oma c luster (Me l 1 1 1 ) . The s e are , o f cours e , naked-eye o b j e c t s , as ar! s ome o ther M e s s i er clusters and the Perseus Double C lus ter , even thou� th e s e lat t er appear wi thin the band of the Milky Way . Many o ther group� s t and ou t well in thei r n e i ghbourhoods when s e en through t e l e s c opes , but o thers are heavi ly affe c t ed by l o c al s t ar di s tribut i on , particul ar1! tho s e c lus t ers in whi ch the s t ars are l o o s ely spread . In such case s the fi eld s t ar s c an pre t ty well overpower a c lus ter , and even s om e rich o b j e c t s c an be heavi ly affe c t e d . At the o ther extrem e we find c lu s t e rs l o cated in regi ons of dark nebul o s i ty , whi ch are vi sually apparen t by a pau c i ty o f fi eld s t ars . Such regions are advantageous , ei ther fu llb blanke ting, or effec tively dimming, numbers of fi e l d s tars and th er e y reducing the i r c ontaminat i o n of a given c lus t e r . 2 . C luster Charac t eri st i c s .

Due t o the i rregular morphology o f open c lu s t ers , the i r s tru c t ural charac teri s ti c s are of great vari e ty , and often reveal sub-groups ?f gl s tar s as well as doubl e and mul tipl e groupings wi thin the overall J.rnare, Fi r s t among the points we shall cover here i s that of overall s t ruCtu

Overall struc ture of C lus ters . , There i s no better introduc tion t o the s tructural vari ati ons dJ. SP l�t p e by o pen c lu s t ers than that furnished by the 2 7 obj e c t s o f thi s typ �o� the N e s s i er catal o gue . The s e range from c lu s t ers o f l o o s e concen t ra,t> such as M2 9 to c ompre s s ed , rich obj e c t s such as M 1 1 . The differen ce S ,

c lus ters of i dentical Shapley type wi ll be a func t i on en t i n Thus , i f we t ake two clus t ers o f Shapley class ' e ' . . apP&7 e c o f d � ds t 2 the i r r e s p e c ti ve di s t anc e s of about 2 5 0 and 9 2 5 pc an at iy affe c t the i r t e l e s cop� c app earanc e . Being the nearer �i l l gr � 0 M 7 virtu ally fi l l s a 1 fi eld ; in c ontrast M 5 2 i s only w o f th e2 0 a; cmi nut e s in great e s t angular si z e , and therefore appear s a b ou t c lus ter-lik e , the angular s eparat i on of i t s s t ars being e roo r i derab l Y reduc e d . con s of open c lu s t ers are o f t en fairly we l l-define d , , Th e b oun dar i e s s an overall e l ongation wi l l be s e en . Thi s wi l l obj e c t any m r d f an ? y due t o the e ffe c t s o f gal ac t i c ro t at i on , and thus b e pr���ril maJ r axe s of many c lu s t ers wi l l show a t endency to be al i gned th e c er tai n ext ent paral l e l to the gal ac t i c p l ane . H owever , i t to a that thi s relation o f maj or axi s t o gal ac t i c plane do e s e ��� :�!ays operate , and differenc e s o f thi s kind may be related in to c lus ter age s . s ome measure f c lu s t er s wi l l b e c ome more V ria tions i n the overal l s tructure o �ent as the large nu mbers o f o b j e c t s out side o f the J.le s s i er a a p i ters are enc ountered , and we can do no b e t t e r than refer to the � b:: rvati ons in the acc ompying catal o gue for the s e vari ati ons to be appreci at e d . Magni tudes o f Open C lus ters . Integrated magni tud e fi gure s are no� avai l ab l e for �ll c lu s t ers , and in particular have n o t been determJ. � ed for many obJ e c t s o f rel a tively recent di scovery . Fo r the maJ orJ., ty o f NGC and I C o b J, e c t s , however magni tude s are avai l abl e . The 2 7 c lu s ters in the M e s s i er catalo � e have a di spersi on o f almo s t 6 magni tudes , the l ower limi t being 7 . 5 mag for M 1 8 . When we consider c lusters ou tside the Messier ob j e c t s , there i s i nevi t ably a c oncentrati o n t � ward � much fainter magnitudes . In the catalogue of open c lu s ters J.n thJ. s Hand­ book the maj ori ty of o b j e c t s are in the 9 to 1 0 magni tude range . Magni tude fi gure s , howeve r , do no t give a meaningful indi cation of the Vi sual appearanc e o f a c lus t e r . Whi l e the magni tudes o f c �u s ter s tars are importan t , o ther contributory fac tors are the d l stri buti on o f the s tars and the charac ter of the c lus ter are a , the lat te r havin for very smal l c lU s te rs where g alre ady been di scus s e d above . Only s t ars c omponent the due to the effe c t s o f di s t anc e , are clo sel y gr�up ed wi l l a magni tude fi gure have much of a bearing , d � e V en then no t a ' great deal . The magni tudes whi ch are o f intere s t o bs erv ers , therefore , are n o t the integrated one s , but tho s e o f u st er st ars . Th e R. ange of C lus t er S t ars . W th th e int rinsic magni tudes of some c lus ter s t ars p e aking at abo lt = �i l� Mv - 5 , the ne are s t c lusters in whi ch such s t ars are ?res ent �i sPlay memb ers of qui t e high vi sual magni tudes . The brJ. gh t e s t et a l n th e P l e i ade s , f o r example , h a s m =2 . 9 6 , and even i n a f a1 t er Of b , m o r e di s t ant clus ter such as M4l the bri gh t e s t s tar s are a. out mv = 6 . 0 , whi l e the bri ght e s t members o f o ther c lu s t e r s J. n

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Obs ervation o f Open Clus ters .

Obs ervati on of Open Clus t er s .

the M e s s i er l i s t are o f t en s e en t o reach m = 8 . 0 . As we shal l v e the magni tud e s o f man y c lus t er s t ars eventually becom e t o o fai n S r e gi s t er in moderat e t e l e s c op e s a s individual point s , but whe r ta e number of them are conc en trat ed t o ge ther they give the appearan ce o f a regi on o f nebul o s i t y .

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I n cases where clo sely grouped , faint s tars show as nebul o s i t the observer i s no t in a p o s i tion to s tate whe ther the s e nebu l ouY ' r e gi on s are due t o unres olved s tars or are ac tual emi s s ion regi o S, In m o s t cas e s the former wi l l be the c as e , and c oncentrat ed observation i n go o d s e e ing wi l l often reveal a small number o f fa t i s t ars wi thin the nebulous are a . A number of such c as e s O ccur i n thn o b s ervation s u s e d in thi s Handbook , and we have examined a few on the Sky Survey print s . In some instanc e s the nebulous regi ons we re ac tual ly r e gi ons of emi s si o n , and the s e wi ll be di s cussed late r , in t ho s e c as e s where the nebulo s i ty was due to unr e s olved s tars we have s e l e c t e d two for c omment .

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The two c lu s t ers in que s t i on are NGC 6 8 1 9 and Tr 9 . In both o f the s e nebulous regi on s were obs erved wi th a 1 0-inch refl e c t o r ; the r e gi on in NGC 68 1 9 being horse sho e-like in shape , that in Tr 9 being s tructure l e s s . Compari son of the drawings of the c lus ters with the Sky Survey image s sho\ojed that in both c as e s the nebul ous regi ons are c omp o s ed o f un r e s o lved s t ars , the concentrati on being heavi e s t in NGC 6 8 1 9 . Finally , we t ake the que s t i on o f the number o f s t ar s t o be seen in c lu s t ers . Count s o f the s e are often made by vi sual obs ervers , �d thi s rai s e s the point o f true c lus ter m embershi p , a point which is enhanced in tho s e ins t anc e s where c lus ters inhabi t rich fi elds , and a m erging o f c lu s t er and fi e l d s tars o ccurs .

As the derivati on of true clus t er s tars i s by no .me ans an easy task for the profe s s i onal as tronomer , i t c an be appre c i ated that exac t de t erminat i on of them i s beyond amateur capabi l i ti e s . The fainter clu s t e r s tars are beyond vi sual obs ervat i on , and de fini tion o f any bri ghter ones c an be hi ghly un c e rt ain . The m o s t that the vi sual obs erver c an achi eve in thi s sphere , therefore , i s to gi ve � indi cation of the number of s t ars that appe ar t o be wi thin the c onfine s of a given c lus t er down to what ever limi ting magni tud e c an c an b e reached . Occasionally a clus ter wi ll be encoun t ered whi ch i s located in a relatively barren fi eld , and here a more defini ti ve r e su l t may be o b t ained wi th s tar coun t s . I t may l e gi t imately be thought that the given angular d i amet er of a c lu s ter c an be used to f i x i t s boundari e s , but thi s i s not th e case . Angular dfame ters of a clus ter c an vary wi dely , dependin g up on the source , whi l e true m embership of many c lus t ers i s s t i l l a l ong way from being final i s e d .

C lus t e r s Associated wi th N e bul o s i t y . d In many c lus ters nebulous regi ons are not indicative of un re so l1 U s t ars but c ons i s t of ac tual nebul o s i t y , and thi s can vary consi d e rfl. y in s i z e and bri gh tn e s s . In many cas e s the nebul o s i ty i s qui t e sm a l l�� apparent dimen s i ons whi l e at the o ther extreme i t i s very exten d e d

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or very faint . In as s o ci at i on s such as fai r l y bri ght si ty can be obs erved wi thout di ffi culty o nebul M 1 6 the tude s , and a fair amount o f detai l can lati rn e Ha and rth o mi d n fro10 e mad out . be s o c i at e nebul o s i t y , whe ther c onne c t e d s na tur al t o as It . th t h e rich regi on s lying t owards the wi , t no r o s ter Us � th i C c en tre and certainly such a s s o c i at i ons are bri gh t gal&C The re �re , however , p l enty o f c lu s t er s immers e d in ob j e c o sn. nebul o s i ty in the anti-c entre regions o f the Galaxy , dark eJDi ss e are always wor th whi l e observing, as in the andt th e k some , i gns o f s frequent s on i ciat so as e s the which s ie �n r i n sui t ab l e t e l e s c o pe s , a ri ch­ apparent e b may tY si O ne pe p o s sibly r e gi s t ering s om e o f the more extended £i d tel e sco the regi on of c lus t ers like Mel 1 5 , where the in ty lo si s sion nebul a i s I C 1 80 5 . l arge areas o f A good exampl e of a c lu s t e r involved wi th and dark nebul o s i ty t gh bri both ere H . 0 8 3 7 NGC s i y osit nebul s , and what appear s t o is s trikingly apparent on pho tograph t h e rel evant entry i n in corded re s i former e h t of be some the catalogue o f clus ters in Part Thr e e . er ei th

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A further sinall group of c lus t elc's in whi ch nebulo s i ty was suspeoted have been examined on the Palomar print s . NGC 2 1 7 4 and 2 1 7 5 , NGC 2 4 6 7 and N GC 6 9 1 0 are the c lus ters , all were found to be associat e d wi th emi s sion , and the obs erved areas of nebulosi ty corre sponded well wi th the image s on the print s . For all its general faintne s s , nebul o s i ty conne c t e d wi th olusters i s well worth s e arching for , and for thi s re ason we li st in the catal o gue any c lu s t er wi th nebul o s i ty connected or in the general regi on , although we have omi t t e d cas e s in whioh the intensi ty l evel o f the emi s si on is t o o low for visual obs ervation . Star Colour s and Flare S t ar s . Although the magni tud e s of mo s t c lus ter s tars are too faint fo r muoh in the way of c o l our t o be s e en , s ome co l our i s ot 1. c e�ble i n certain cas e s . Indivi dual e xamp l e s are to b e ound 1 n the catalogue , but in pas s ing w e can mention exampl e s in the Perseu s Doubl e C lus t e r , where at the r e s p e c t ive centres to be s e en numbers o f red and blue s t ars wi thin qui t e smal l � e e,... ons , a nd whi ch pre s ent an impres s ive spectac l e . Flare stars are to be found in many clu s t ers ; of the UV C e t t p e , th ey app ear i n NGC 2 2 6 4 , M 42 and the Taurus dark clouds . an MY unfY ' SUCh as V3 7 1 Ori , are sources of radi o emi s s i o n , but r tun at e ly the maj ori t y reach very low magni tud e s even a t � �a m� . Two , however , in the Pleiades com e wi thin reach of t Whi l U . t e le s c opes , and d e t ai l s are shown overl e af in Table 4 , � th th1 gure 6 , al s o overl eaf , shows a chart of the Pleiades e P o s i t ions o f the flare s tars p l o t t e d .

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Obs ervation o f Open C lu s t ers . Table 4 . Flare s t ars in the Pleiade s . ( 1 9 50 )

S t aF RA 03 42 . 6 A :B 03 4 3 . 4

Dec +2 3 2 9 +24 3 0

Spec dK5 e K7

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Fi gure 6 . 3 0 s t ars i n the P l e i ades fi e l d t o magni tude V = 7 . 54 . S tars 1 and 2 are n o t members , and t h e p o s i ti on s of the two flare s tars are marked A and B .

GLOBULAR CLUSTERS .

gory o f c e l e s ti al obj e c t recogni s ed as gl o bular wa n o cate e e r m . H erschel firs t used the d e s cri p t i on in hi s Tb s un il W clu s t e r e s o f n ebul ae of 1 7 8 6 , and even there the d e s cripti on d o e s c atal o gu s ma tch the di s tinc t i on we apply t o day . al way no t omega C entauri i s a gl obular c lu s t e r , but t o o w kno W that e s t ar - hence i t s t W bse r vers i was c onsi dered a si ngle ancien a o f 1 60 3 . The fi r s t Uranometri s hi in Bayer by omega s t on a enume r ti on of thi s o b j e c t a s a ' n ebul a ' ( o r ' lucid spo t like a rec 0 examined i t t e l e s c o pi c al ly at s t ) was due to Halley who clo u Halley who in 1 7 1 4 firs t di s c o vered o s al was t i and , 677 1 H e e : in i t t l e Patch , but i t He r cule s , whi ch he d e s cribed as ' but a l erene s s i and the Moon Sky the when Eye Naked the ows itse lf t o absen t ' H o we ver , the fir s t gl obular c luster t o be di sc o vered as a , Abraham Ihl e , ' ne bula' was not found by H al l ey , but by the German dent whi l e i c ac by apparently , arius t t Sagi in M22 wbo c am e upon ' s two s ey e l t a al d H of the en twe Be . 5 6 6 1 n i Saturn g rvin obs e globul ar cluster di s c overi e s ano ther was found by Go t t fri ed Kirch in 1 7 02 ; thi s was M5 in Serpens . I t was n o t un til 1 7 4 5 that the tall,. of globulars was rai s e d to six , when de Ches aux c ame upon M4 in Scorpio ( which he des cribed as ' smal l , whi t e and round ' ) and M7 1 in Sagitta. The next y e ar , 1 74 6 , s aw the addi t i on of two more globulars , M2 in Aquarius and M 1 5 in P e gasus , bo th being picked up b7 the French as tronomer Maraldi whi l e l o o king for de Ches aux ' com e t of 1 74 6

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Max 1 3 .4 1 3.3

gI ST

PART TWO

25

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�ing his expedi t i on t o the C ape o f Good Hope in 1 7 5 1 - 52 , the Lac ai lle added five new gl o bulars to the known t o t al , the s e be ing NGC 1 04 ( 4 7 Toucani ) , NGC 483 3 , NGC 6 3 9 7 , M 6 9 and M 5 5 . The on tribut i on o f Me s sier t o the gathering o f new glo bu l ar c lu s t ers � m press ive : he began by picking up e i gh t : M3 , M9 , M 1 0 , M 1 2 , M 1 4 , M ' M2 8 " M3 0 , be twe en 3rd May and 3rd Augu s t 1 7 6 4 , and there after h e an d Mec hain be twe en them c ontribut ed ano ther t en by March 1 7 8 1 . A bb e

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described in the H i s t ori cal Revi ew o f Open C lu s t ers , the mo no m en al gath ering of nebulae by the elder H erschel brough t many re h ad t glo bu lar c lu s t ers into vi ew , but a more defini tive analysi s await the inven tion of the spec tro s c ope and i t s app l i c at i on n omy by pioneers like Wm . Huggins , and the c l as sification of B t e ar sp e c tra by Sec chi . Further pro gre s s followed the i o n o f RH Lyrae variabl e s t ars in gl obular c lus ters by S.l. B a ey in 1 90 0 , the introduc tion o f the Hertzsprung-Ru s s e l l diagram n 1 90 5 , and , in 1 9 1 7 , the deri vation o f the di s tance o f ao l a r sy s t em t o t h e nuc l eus o f the Gal axy by Shap l ey . For thi s di a t a nc et e rminati on ( no w much revi s e d ) Shap l ey made a s tudy o f dl a bu t i o o f gl o bular s , no ting their preponderan c e i n the � gr re � nUol eu s o f g1 0ns of the s ky , where , o bs cured by dark nebulae , the Galaxy i s s i tuat e d .

to as��� re c o gni I

i th e th e : � SCO-OPh_�

26

H i s tori cal Revi ew.

Fur ther impetu s was gained in the s tudy o f gl obular clus t e r s by WaI t e r Baade ' s analy s i s of s te l l ar populations in 1 944 . Sinc e th e n due primarily to the large-scale plat e s of the S ky Survey , fur th er' globular c lu s t er s have been i dentifi ed wi thin the Galaxy , whi l e plates taken by l arge refl ec tors have revealed many of the s e ob j ec t 8 in external galaxi e s .

I lITRO

N. DU C TIO

5 . GALACTI C GLOBULAR CLU S TERS .

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gl obu l ar c lu s t ers we are c onc erned wi th o b j e c t s that are t rin s i c lumino s i ty , great age and , in contras t to open n i o f hi gh do no t show space di s tri buti on that i s l argely c onc en­ o lul t e r �� the gal ac ti c plane . tra t e d s are known in external galaxi e s , globular Whi l e open c luster more numerous in thi s context , and in tho s e ch mu re a s oluS t e r globul ars are sui tab l e for d e tai led s tudy , are very ere vh o as l for c ompari son wi th c lu s t ers in the Galaxy . The s e extra­ ac ti c glo bul ar c lu s t er s wi l l be c overed in more d e t ai l in Chapt er 6. Th e s tudy o f glo bular c lus ters take s us back t o the early oluti onary s t age s of the Gal axy , and , among o ther things , f orm ati on derived from s tudi e s of gl o bulars i s o f importanc e in that knowl edge o f the early chemi c al c ompo si tion of the Gal axy i o an be obtain ed . Thi s chap t e r w ll be concerned wi th the vari ous gl o bular c lu s t ers , begi nning wi th c l as s i fi c ati on e s of erti prop and c oncluding wi th c o l our-magni tude di agram s an d clus t er age s . From the point of vi ew of spac e , c overage of the.s e aspe c t s mus t o t necessity b e bri e f , but hop eful ly an adequate pi c ture o f the s e obj eots wi l l be po'rtrayed . Wi th

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Classificat i on .

The only c l as si fi c ati on o f gl obular clus t ers that mo s t amateurs will be fami l i ar wi th i s that of Shapley, and as thi s i s purely a struc tural scheme , i t i s of u s e to vi sual obs ervers . Detai l s o f o ther clas sifi c at i on s wi l l b e given b e l o w . Shapl ey ' s c l as s i fi c at i on i s b ased upon t h e degree o f c onc en­

tration shown by cluster s t ar s , and i s divided into twe lve 01a 8 8 e 8 , ranging from Class I - the mo s t hi ghly c on c entrated , t o Clas s XII - the lowe s t c onc en�rati o n . Thi s scheme shows the wi de

range of star d i s tribution in globular clus t ers , and , as wi l l be I ho wn in Chap ter 8, c oncentrati on c l as s , al ong wi th o ther fac t ors , h as a con side rab l e b e aring upon re sul t s o b t ained by vi sual obs er­ ve s . Al so affe c t e d by the s e s truc tural properti e s are matters at in g to the d i s c overy o f glo bular c lu s t ers on pho t o graphs en by large t e l e scopes . . n ast ronomy , c l a s s i fi c at i on of obj e c t s i s nowadays not always a l"Uc tur e"rel ated proc edure . We have only to think of Seyfert &xi es in thi s c on text ; ini t i ally the c l a s s i ficati on was purely I t l"U t 8c c ur al , but i s now s e en as a spec t ro scopi c c onc e p t . Spec tro­ c c l as s i fi c ation c an relate c on s i d erably t o di fferenc e s in Ob c al con t ent between di fferent clas s e s of obj ec t , and thi s i s le en th e field o f globular c lus ters . A c l a s s i fi c a t i on scheme to� obu l ars has b e en deve loped by W . W . M o rgan , and thi s i s tto. up on the integrated spec trum o f a clus ter . The s cheme runs I t h r ough to VI I I , the former indi c a.t ing a c lus t er wi th very -.t al l i c spec tral line s , the lat t er a cluster who s e spec trum

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28

Galac t i c Globu lar C lu s t ers .

Galac t i c Glo bular Clu s ters

sho.w s the s tronge s t m e t al l i c i ty. The u s e fulne s s o f Morgan ' s m e th bear.s directly upon the probable vari ations in c lu s t e r format i on o d during the early evo luti on of the Galaxy .

I t has b e en known for s ome t ime that tho s e s t ars in the Gal a who s e spec tra show a hi gh m e tal conten t are young o b j e c t s . O ld e o b j e c t s , among whi ch are included gl o bular c lu s ters , are al l kn o t o be metal-po o r , thi s being a produ c t o f their formation in th e� e arly epochs o f galac t i c evo lution , at a time when the inter s te l l medium had n o t b e en enri ched by heavi er e l ements formed in s t e l laar interiors and di s pers ed by various mean s back into s pac e . Howeve s p e c tro s copy o f globular clus ters showed that differenc e s occuri � n in c luster s p e c tra c ould no t be reconc i l ed wi th such a s imple s t at ement as old = me tal-p o o r . From thi s }10 rgan ' s c l a s s i fica t io n evolve d . The s e vari ations i n c lus ter s p e c tra indi cate differ enc e s in c lu s ter formation as a func t i on o f galac tic l ati tude , vi z . , th e c lu s t er s at l o w galac t i c lati tudes show s p e c tra o f higher metal c on t e:nt than tho s e at higher galac t i c latitude s . A likely explanation o f thi s i s that the low lati tude clu s t e r s may be the result of qui cker s t ar formation and thus higher m e t al enri chment o f the inter s t e l lar m edium . A similar clas si fi c ation o f gl o bular c lus ters i s the Deu t s ch-Kinman sys t em : A = medium me tal abundance ; E = l ow m e t al abundanc e and C = very low metal abundanc e .

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Glohular c lu s t er s are al s o divi ded into O o s t erho ff groups , a s cheme whi ch divi d e s c lu s t e r s into two c las s e s and i s based upon the typ e s of RR Lyrae variab l e s tars in a given c lus t e r . In these c lu s t er s RR Lyrae s tars are of two typ e s : RRc variab l e s have periods of l e s s than 0 . 4 days and have smal l ampli tude s ; RRab variables show peri o d s o f over 0 . 4 days and have ampl i tudes up t o 1 . 7 magI RRc vari abl e s are on. average b luer o b j e c t s than RRab ' s . The c lus ter s are divi ded into two group s ac c o rding t o the number and mean period o f their RRc and RRab variabl e s . In Group I RRab s t ar s are pre s ent i n l arger numbers than RRc s t ar s whi l e in Group 1 1 RRc s tars are twi ce as numerous as RRab ' s . Exampl e s of Oo s t erhoff Group I c lu s t ers are M3 , M 5 and NGC 6 2 2 9 , whi l e O o s t erho ff Group 1 1 c lus t er s number among th.em M2 , M 1 5 and N GC 5 4 6 6 . I n pas sing i t i s worth mentioning th at 9 �� o f known c lus ter vari abl e s are RR Lyrae s t ar s , and that cl us ters rich in the s e mainly be l ong t o the halo popUlation of c lus ters i n the Gal axy , obj e c t s of low m e t al abundanc e . 2 . Relation o f Globular Clus ters to the Gal axy.

29

I f one l o o ks at a p l o t o f gl obul ar c lu s ters in a s t ar at las , and c ompare s thi s wi th the di s tribution o f open c lu s ters , the differen c e s are immedi ately apparent . The gl obulars inhabi t th e c en tral and halo regi on s of the Gal axy , and the di spersion in z i s c orre s p ondingly extreme . Lower figur e s for globular c lus t ers sh oW z = 0 . 1 and upper fi gure s z = +64 . In Fi gure 7 overl eaf, the di s tribution in the Galaxy of 1 2 9 gl o bular c lus t er s i s shown , th eSe being t aken from the catal o gue o f Kukarkin ( 1 9 7 4 ) . I n the diagr am the c oncentration of c lus ters at the c entre of the Gal axy i s w e l 1 �

. full effe c t s o f heavy . n the s e regi on s that the the d �. t � s . � t rstel lar mat ter i s mo s t prono unc e d . S tu d �· e s 0 f an o by n e show c onsiderable ab sorp t i o n , but . :- d �� v�. dual c lu s t ers ' .. a t i n s e Jlu o bSe � gi o n 0 f �n S vi s i ble wavel ength s , fGr there in ter s regi e re h e s e c 1u s t ers an area defined by gal ac t i c Within not do � l ea s t t that a u s t e rs l c m i de 8 . 4 t o 3 5 6 . 0 , are t o b e o longi tu s e t 0 - 2 . 7 , gal ac t c ar e so · de +1 . 7 s t ers , the s e b e �ng lu c d cure s b o tu ely i l at be 0 f extr em m u the in only n le ctab a d fo un b s orp t i on that they are dete d d ent rec e e t qui are , Terzan e n by ted c e t e lus t ers , d r edd es s. re d . ranks of gal actic gl o bu�ar c lus t er i nf r a e th to s i on t di d

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Fi gure 7 . Gal ac ti c di s tribut ion o f 1 2 9 gl obul ar c lu s t ers . The Palomar clu s t e rs Pal . 3 and Pal . 4 are indi c at e d on the chart .

� S t ructure of Globular Clusters .

The morpho l o gy of ' c las s i c al ' gl obular c lus ters , exempli fied by o b ,l. ec t s s as M 1 3 and omega C en is fami liar to the amateur . Th? maj o ruch , i ty o f the 11e s s ier c lu s t � rs are o f Conc entrati on Clas s V h l.l e th e low oncen C a with , 5 5 � ra e s t c las s for the s e c lus ters i s M y tion C las s of XI and being of such l o o s e s tructur e i s easil Olve d wi th the mOder � t e t e l e s c o p e s , and even on pho t o graphs fe renc e in th e s truc ture of thi s clu s t e r , when compared wLth m o re h e aVi ly conc c l ear . c lu s t e r s , i s entrat e d � Ou t o f t h e 1 3 0 odd gl obular c luster s known in the Galaxy, there e l even of are amo n,g Concen tratio n Clas s XI I , and of the s e s even th l The s e O eU s ters di s c overed on the P al omar Sky Survey p l at e s . Cl a t the M 1 3 f o s t c e j b o d from t i en s differ sp l ay s truc ture very 1 1� r • be ing o f very low dens i ty , s o l o w , in fac t , that they would

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30

Gal ac t i c Globular Clust ers .

Galactic Glo,bular Clu s t ers .

be di s rup t e d by gal ac ti c ti dal force s i f they made t-O-O clo se an a'Ppro ach . Such clusters , lying we'l l out in the gal actic hal o , ar e exemplified by P al omar 3 and Palomar 4, whi ch are marked on th e chart on page 29 . All o f the halo globu l ar c lus ters , obj ects wi th l arge z , h ave l arge intrinsic diame ters , P al omar 3 , for e xampl e , having an ac tu.a di ame t er o f 6 1 p c . C ompare thi s wi th clu s t ers of smal l z , such a l NGC 6838 ( z = - 0 . 2) whi ch has an intrinsic di ameter o f only 6 p es The re ason for thi s is that gal ac t i c tidal forc e s l imi t the r ad i i o f mo s t clusters , and i f the s e forc e s are small a given clust er wil l show a l arger intrinsic di ame t e r . The radii shown by dis t an t Palomar c lus t e r s in the gal ac ti c halo are e xp l ained i f they have never c om e cl o s e r than 9000 pc to the gal ac t i c centre .

The inte grated pho tographi c magni tudes o f P alomar c lus ter s are of the order of 1 5 mag, y e t they are by no means e asy t o detec t . The r e as on for thi s i s their l ack of s t e l l ar conc entration , and hence their inabi l i ty to s t and out in di s t ant s t ar fi e l d s . Obje ct s such as M3 and 1'11 3 are more p opul ous in s t ar s by a fac tor of 1 0 than are the halo P alomar clu s ters . Six o f the l at t er are barely recogni s ab l e on the Sky Survey plate s ; all are of Concentration Class XII and l i e in regi ons unaffected by gal ac t i c, o b s curation.

4. Colour-Magni tude Di agram s .

We have s e en in Part One ( Table 2 ) tha:t; halo gl obu l ar c lusters form the extreme Populati on 1 1 regions of the Galaxy; thi s shows t hem t,o be extreme ly o l d obj e ct s , wi th age s of the ordex of about 1 0 10 yr .

-2 Fi gure 8. C-M di agram for M 1 5 . MS refers to the main-sequence , HE the hori zontal branch and GB the giant branch.

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31

be tween thi s and the di agram shown for the

e l and t h n page 13 is immediately apparent . Note the posi t i on o f e ad ei _ e qu en c e turn-off point for M15 a t Mv +4 , which i s Pl th e . m ' ve o f i t s o l d age , f o r as w e have s e en , the l ower the turn­ 1t in d1 c a . n th e older the c,lu s t e r . Compari son of the M15 di agram wi th o f f p Ol M 67 on page 1 4 shows s ome simi l ari ti e s ; bo th c lus ters f that O o st s t ar s t o the gi ant branch . For determinat i on of c lu s t er havi n no si ti e s and t emperature s o f s t ars both on and below h lumi � S u - off are nec e s sary , p lus di s t anc e s and m e t al abundanc e s . th e t are theore t i c al evoluti onary tracks for s t ars o f the

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Also re qui red al c ompo s 1' t 1' 0n and mas s . n ec e s sary chemi c l ours of c lu s t e r s t ars , whi ch wi th pho t o e l e c tri c ally d e t ermined c o e t al content of s t ars m , emperature t ar l l e t s of e asur re a me and computed theore t i c al model s , a great spectra r thei from d ive e unt of data c an be c o l l e c t e d . However , many probl ems exi s t in the uisi tion of such informa � i on , in p arti cul ar that of , d � rivi ng accurate magni tud e s for fa1nt c luster members . In addl t 1 0n , the pro cess of pho tome try is o f t en rendered di ffi cul t due t o the effe c t s o f crowdin g by o ther s tars , p articul arly in tho s e c a s e s where the pho tometry is undertaken c l o s e t o the c entre of a c lu s t e r .

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Evolution of Globular Cluster Stars . At first sigh t the col our-magni tude di agram for M15 on p age 3 0 appears rather anomal ous ; a turn-off point i s vi sibl e , and ye t there are s till luminous s t ars t o the upper l e f t of the turn-off . In order t o expl ain thi s we shall now define the proc e s s e s through whi ch stars in a globul ar c luster pass in order t o regi s t er on such a colour-magni tude di agram as shown in Fi gure 8 . Th e gr eater p art of a s t ar ' s life time i s spent on the main­ s equenc e , an d we now wi sh to know the evo luti onary s e quence from the om � ent when a s t ar l eave s the main- s e quence and move s into the gi ant r an ch region o f a c o l our-magni tude di agram . The regi ons of the d we shal l be conc erned wi th are the hori zontal branch and the s �nym� toti c branch , whi ch is shown immedi ately above the gi ant branch Fl. gure 8.

i agram

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le a�i ng the main- s e quence , a s t ar wi l l spend about 10 9 yr s�b g1 an t branch , whi ch l i e s below the giant branc h . During thi s er i n to � e � od hydro gen undergo e s nuc l e ar reacti ons whi c h transform i t � um , thi s o c curing in a shell surrounding the c ore of the B t a.r 1 ch at thi s time c ompri s e s inert helium . Fo l l owing thi s ' Pha. s w almo s t i d ent i c al period o f time i s spent on t he giant an b r an h . e

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' Even tua1 1 y a s t,ar wi. ll r e ach a peri o d in i t s evo lut i on where i t "il l a e t he h � ar , at the uppermo s t point o f the giant branch . At thi s point e flash • • l , l n the core begins burning, an event known as the ' he l ium t io n l l e the s e reac t i ons are t aki ng p l ac e , the s t ar wi l l swi tch n the c o l our-magni tude di agram and app e ar on the hori zontal I � s Po s 1, t i on in thi s p ar t o f the di agram wi l l depend upon the

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32

Galac t i c Glo bular Clusters .

6.

amount of mass i t has l o s t during the red giant phas e ; the gr e at mas s lo s s , the bluer the po si tion i t wi l l at tain on the hori z on t tl branch . Onc e the helium in the s t ar ' s core has been consumed . i t wi ll 1 the hori zontal branch , having spent a l i t t l e l e s s time there th an e a�: the giant branch . The s t ar ' s next move i s to appear on the aS Yllrp t on branch o f the di agram , i t s po si tion here once again being det e rmi tlc � by i t s mas s .

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A s t ar on the asymptotic branch i s a very old obj ec t , and i t i s l ikely that a s t ar in the upper reaches of the asymp totic branc h m ve� undergo a phase o f thermal instabi li ty , and henc e l o s e a cons id e ra perc entage o f i t s mas s . I n Vo lume 2 o f thi s seri e s i t was des cr i bed p l ane tary nebulae may evo lve from red gi ant or supergi ant star s , and ', thi s c ontext i t has been shown by theory that the result of the t h e rm;' i n s t abi l i ty of an asymptotic branch s t ar may be pul s ations analo gous : tho s e that occur in Mira-type variable s t ars . During thi s pro ce s s , th ' maj ori ty of mat eri al lying above the hydrogen shel l o f a star may b e E e j ected , and i t i s po s sible that thi s pro c e s s may re sul t In the form­ �ti on o f a plan e t ary nebul a . P l anetary nebul ae are not known to be numerous in gl obular c lu s t e rs; up unt i l qui t e rec ently , i n fac t , only one was known to be as soci ated wi th a c luster , Ps 1 in M1 5 . Lately , however , i t has been shown that there m ay be a second planetary in M 1 5 , and i t i s pos sible that it ma) be as s o c i ated wi th an X-ray sourc e thought to l i e at the c entre o f the clu s t er . In 1 97 7 a p l anetary was found CJcbout 3 arcminu t e s away from th: globu l ar clus ter NGC 6401 , and that i t i s p o s si bly a c luster member. X-Ray and Radi o Sourc e s in Gl obul ar C lu s t ers . A number of glo bular c lu s ters sho,,, evi denc e of X-ray emi s sion , arnon: them NGC 6440 , NGe 6 44 1 and , as mentioned above , M 1 5 . 'rhe s e source s IDa; indi c at e that globul ar c lusters of hi gh conc entration have managed to retain some gas , al though currently the mechani sm responsible f or the X-ray emi s si on i s not certai n . One idea pu t forward i s that of the exi s tence of black hol e s at the c entre s of X-ray c lus ters . Some globu l ar c lu s t ers are known t o have radi o sourc e s in th e i r b respec tive fi elds , and whi l e i t i s possible that the s e sourc e s may e as sociated wi th the c lu st ers , i t i s al so po s sible that they may b e extragal ac tic in ori gin . Among the radio globul ars are some of t h e tile 11e s si er obj e c t s , including M2 , M3 and M92 . In the latter two cas eS r adio s ourc e s are simi l ar to tho se exhi bi ted b y c ertain p lan et arY witP nebul ae , and thus i t i s p o s s i b l e that more p lane tari e s assoc ia t e d gl obular c lusters awai t di sc overy opti c al l y . At the pre s ent ti me , however , no thing i s defini te i n thi s fi e l d .

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33 GLOBULAR C LU S TERS I N EXTERNAL GALAX I E S .

j ec t s o f hi gh intrinsic lumi n os i t y , globular clusters Be i g o b l e out to consi derable di stanc e s . We therefore find c tab ar e d eo � onl Y ass o c i ated wi th galaxi e s in the Local Group , but al s o n tb e� lusters such as the Virgo and l ge ell ip t i cal galaxi e s in c tic vi tb globul ar c lus ters are o f . Such extra-galac rs te lus c gyd r atan c e a s they can b e uti li sed t o derive such informati on as i �por se s ' of giant galaxi e s , and the d i s tance modul i of galaxy �as th e t er s . c lu s probably fami l i ar wi th pho tographs of the Mo st amateurs are and have no t ed the gre at swarm of globular M87 , axy gal E an t i s tri buted around i t s outer regi ons . O ther bri ght , E d rs te us c gal axi e s in the Virgo cluster of galaxi e s are s e en to be very t i n globulars , �n parti cular NGC ' s 4374 , 4406 , 447 2 , 4486 and Rich in gl obular c lus ters as the s e are , the sum t ot al obular c luster popUlation i s a l i t t l e over half the gl ir the f o a globul ars in M8? Where the parent galaxy i s an E-typ e , of n ber above exampl e s , a sui t able pl ate/fi l ter i . e . , red , as in the c o�binat ion is nec e s sary , in order to reduce contaminat i on by galaxy mate rial . In Fi gure 9 we show the di s tribution of 60 clusters around the Virgo C lu s t er galaxy NGe 42 1 6 ; the di spersion in magni tudes of the s e clusters i s qui t e l arge , the bri ghtest cluster having a magni tude o f 1 7 .46 and the faint·e s t, a magnituvde The di fferenc e s in bri ghtn e s s of the c lus ters i s no t o f 2 2..84 . &boa in the fi gure

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34

7. CATALOGUES OF GLOBULAR CLUSTERS.

Glo bular Clusters in External Galaxies.

Coming now to the Local Group of galaxies, we find that glo bu l clusters are associated with a wide variety of galaxy types, r an � from the Fornax dwarf galaxy to M31 . In particular, many globula gl�1 are connected with the Magellanic Clouds, numbers of these bein r a objects, and the brightnesses of these clusters are such that t�e N� have been the subject of Colour-Magnitude diagrams by Arp Wo oll �� and others. Examples of fairly loose globular clusters ar ; also � be found in the Magellanic Clouds, objects such as LW 441 and LW However, in these and other cases, the level of detectability i s 46), greater than for the Palomar clusters, and it must be remembered th some of the latter are possibly at greater distances than the two a; Magellanic Clouds. One difference between globular clusters in the Galaxy and tho in the Magellanic Clouds is that the latter harbour b 6ue, apparen ��Y young, clusters with lower age limits of about 5 x 1 0 yr. Som e or these young clusters have a stellar content similar to open clustera in the Galaxy, objects such the Perseus Double Cluster and the �leiades. Study of these clusters in the Magellanic Clouds is de emed �mportant due to the fact that they can give an insight into the conditions in which globular clusters can form. Such conditions are extant in the Magellanic Clouds, but not, of course, in the Galaxy itself . Briefly we shall now consider other globular clusters associated with Local Group galaxies, and at this point we take leave of the clusters with NGC designations, apart from the isolated instance of NGC 1 049 , the brightest cluster in the Fornax dwarf galaxy. NGC 1 47 and NGC 1 85 have small retinues of globular clusters, ranging from diffuse objects to more compact, higher surface bri ght­ ness objects. A solitary cluster lies on the west border of the Wo l� Lundmark-Melotte (WLM) . galaxy. For the largest numbers of clusters associated with a Local Group galaxy, we turn, inevitably one feels, to M3 1 . Currently a search for new clusters is in progress, and to date has yielded a large number. Early searches for M3 1 clusters, however, go back to Hubble' s observations of 1 932. M3 1 is a massive galaxy, as is M87, and both are rich in glob ul ar cluster � . It now �ppears that globular cluster membership of a galaxy �s a funct�on of galaxy mass; hence all massive galaxies should play host to a considerable number of clusters . The forego ing, by implication, shows that galaxy type is unrelated to cluster numbers, and in this context we have only to recall the large numbers of clusters associated with massive galaxies in the Virgo Cluster, in particular M87, where the number of clusters known is very high , being of the order of 2000. 0

35

of globular clusters registered a fairly high arlYgecatofalogues are currently known; Melotte' s list of 1 9 1 5 that those perc e nta83 clusters, and by 1 930 Shapley had compiled comprehensive a shO�efor 9 3 objects. In this catalogue, Shapley considered 7 of the d�t: d obje cts as doubtful, but currently these are all considered to 1 1 8 �o bular clusters, and include NGC 1 6 5 1 , a cluster in the Small b e g ic Cloud. y.1a.gell an 3, we have remarked that correct classification of most In Chapister sight, a simple matter, assuming that the only at , �� terirsa is thatfirst This, however, is not - a valid method, morphology. of cr1 �e factor of the stellar content all-important the does, it as g d�n�in in classific.ation have, in difficulties years the Over t . ers us l o was undecided whether to Shapley example, For resolved. n bee neral NGC or the loosest globular, cluster open richest the , as 2477 � as ro cl object is listed as the former type of object . A but currently ethis is NGC 2158, once thought to be a probable globular, rurther examplas an open cluster . The stellar content of NGC 2158 is seen w no ut b NGC 752 , but morphologically the two clusters are of that to ar simil pole s apart . In the 1 960 ' s a supposed globular cluster, known as the ' Russian Cluster' , was studied, and finally turned out to be a distant cluster of Galaxies . The three main catalogues of globular clusters which have appeared over the last 15 years are those of Arp ( 1 96 5) , Alcaino ( 1 973) and Kukarkin ( 1 974) . The number of clusters listed in these varies between 1 1 9 and 13'1. In his catalogue of galactic globular clusters Up includes NGC 1 841 , which is now c.lassed as a member of the Magellanic Cloud system . Also, when Arp compiled his catalogue, a number of heavily obscured clusters, detectable only in the infrared, had yet to be discovered. In the NGC , an object classed as a globular cluster is NGC 6256. J.10re recently the exact nature of this object has been uncertain, but it has been proposed that it is possibly a he avily reddened globular cluster at a distance of about 8 kpc ; at present this object appears only in the catalogue of galactic glo bular clusters compiled by Kukarkin . t Finally, in this brief survey of professional catalogues, we come e Catalogue of Star Clusters, Associations and Groups (Alter, ear� th al ! 1 970) mention of which was made in Chapter 3 . Here 1 2 objects d as uncert �in open clusters, and all are to . be found in t�e c a� allo� ste gues of galact�c globular clusters of Arp, Alca�no and Kukark�n. Fr amateur, the percentage of galactic globular clusters �hi � artheeobservable nUm� out of those currently known is quite high . The �� of g lobulars listed in Atlas Coeli is 1 00 , and 60 of these are � str . �30o �buted north of the mean declination limit of this volume, at wh I n Chapter 3. mention was made of NGC 6 558 and NGC 6642 , both i c� are globular clusters but have been included in the list at C el nUmbo � open clusters. Along with these two objects, there are a �d �� of other omissions and an error in the Coeli globular clusters, ase are shown overleaf in Table 4. E

8.

Catal o gu e s of Glo bu l ar C lus t er s . Table 4 . Errors in C o e li Gl obular Clus t ers . NGC 6 2 56 Omi t t ed . 6� 80 Omi tted. 1 7 h 45 . 7 -60 0 4 5 ' Peculi ar galaxy partly obscured by a l arge patch of dus t . NGC 6 5 58 Omi t t e d ; shown i n Coeli o pen c lu s ters . Omi t t ed . I C 1 27 6 NGC 6642 Omi t t e d ; shown in Coeli open c lus ters . NGC 6 684: Omi t t e d . NGC 67 1 2 Omi t t e d . NGC 67 1 7 Omi t t e d . O f the known gl obular c lu s ters , there are 27 whi ch are comp le tel Y beyond vi sual observat i on wi th any t e l e s c op e . The s e inc lude the P al omar clusters and tho s e obj e c t s d e t e c t ed in the infrared . D e t ail s o f s ome of the l at ter c an be found in Terz an , 1 97 1 , As tron . & Ast 7 0P�Y s . 11, 477 . � �urther pUbli c at i on of inter e s t i s Hogg, 1 96)1 A B� b l�o graphy of Ind�v�dual Globular Clu s t ers , Univ . of Toronto Pre s s .

O B SERVATI ON

OF GLOBULAR CLUSTER S .

37

T ON . I N T RO DUC I Th e numbe r o f gl obular clust ers that c an be obs erved vi sually in y is considerably small er than the number of open clusters . th7 G al ax to the fac t that l e s s of the former are known to exi s t, ; due s Th� i the r hand a hi gh perc entage o f the gal ac t i c gl obular he o t,e l e s cope s . us t er s are observable wi th moderate aperture Di f fe renc e s are very apparent, b e tween open and globular clu st er s text o f r e soluti on . Admi tt edly many globulars wi l l al low �. th e con full r e s o luti on t o be obtained , but no t al l , and in many Y all u t V c an be sai d t o be di s appointing obj e c t s when they W ays gl obul arswi th the vari ed morphology of open clusters . Never­ ared omp re c hel ess , att em p t s t o re s o lve the more r e c alci trant gl obul ars are wel l wor thwhi l e , and the fact that in many cases the obs erver i s r eso lvi ng stars at l arge di s tanc e s wi l l add intere s t to the proc edure . While observers si.tuated in northern l ati tude s have no real equival ent o f omega Cen avai l able to thei r tele scope s , they do have impres sive clu s ters such as M5 and M1 3 wi thin e asy reach of thei r instrument s . Furthermore , t h e 28 gl obul ar c lusters i n the M e s s i e r catalogue are all obs ervab l e from the southern par t s o f the Bri t i sh Isles ( some admi t t edly wi th di ffi cul ty ) and the se clus t ers furni sh an excellent introduc tion t o the se obj e c t s .

��

�

�

:

For the remainder o f thi s chapter w e shal l be c onc e rned wi th cluster vi sibi l i ty and r e s o lution in d e t ai l . In the pro c e s s we shal l cite a selec tion o f observati onal re sul t s and di scus s the problems involved by enli s ting t h e ai d o f currently avai l ab l e data. 1 . Intri nsic Fac tors . Co nc entr atio n Cla ss e s . Det ai l s o f Shapley' s clas s i fi c ation o f globular c lusters by the d egr ee of conc entration have b e en given i n Chapter 5 . In all c as e s the c onc e ntrat i on c l as s o f a c luster wi l l have a c onsi derable be arin g upon its vi sual appe aranc e , and we have already s e en that o a e ly- struc tured halo globulars at, l arge di s tanc e s are only e ec tab le pho tographi cally . Th e mo re conc entrated a cluster i s , the higher the surfac e bri ght­ n i t wil l di spl ay , and i t wi l l con s e quently be obs ervable lly at qui t e a large di s t ance . The most di s t ant clus t er in M e a� s � e r ' s c at a 1 ogue �. s M 7 5 , a t ab ou t 3 5 kpc , and the c oncentrat i on cI a o f I assi � ed to i t ai ds in i t s vi sibi l i ty . For c lusters of lo o c onc entrat�on, v�. sual appe aranc e and any r e s o lution wi l l d e p e d up 0 ;,- g � n the i r di stanc e s and to what extent they may be affected ac h c obscuration. Such c lusters in the !l1e s s i e r c atalogue 8'\lOh ar e e asy to obs erve and resolve are al l relatively c,l o s e , as M 5 5 ( C l as s XI ) whi ch i.s 4 . 6 kpc d i s t ant .

��

,,�: a

:: "'lu. �\

38

Obserration of Globular Clusters .

Observation of Globular Cluster:a .

Integrated Magni tudes r 4 we mentioned that magni tude figure s for extend . In: Chapte obJect s often bear little. relation to their appearanc.e at th ed eyepiece . In this field the struc'ture of a globul ar c luster �as an importan t functi n , as discuss ed above. However no one � parame�er of any o?Ject can really be considered in., isolati on and th�s is shown ln the present section of chapter whe're although we are dwelling upon magnitudes , we this do not str ay , far from the concentration classes of clustersstill . seen that. distant , low concenx,ration clust.ers are . We have:mobserv �lsu;ally ab�e, . and this , it must be stressed , is tota11Y lrrespect lve of thelr �ntagrate d magmitude s , which are not particularly low. If we were to apply integrated magnitud as a criteria of visibili ty , then the cluster Palomar 5 (ves only 1 1 6) should present virtuall y identica l visibili ty to an object like' NGC 64,2..:6 (V 1 1 . 48 ) . This is no t the cas e , however , and the d � termining factors whic� make this so are the respectiv e angul ar dlameters and conc'e ntratl0n classes, plus , in the c.a se of Palom 5 the heavy star distribution in its neighbourhood .. For Palomar ar 5 we have the following: c;()ncentration class XI I ; angular· diameter 1 0 ' �3 . For NGC 642b : conc:entration class I X ; angular diameter 2' .2. I� �s easy to see from this that the large differenc es in. angular Slze between these two objects is particularly crucial wh.en it is allied to the respective concentration classes . Just how sparse in star distribution a c:l ass XII cluster can be is shown in Figure 1 0 at the conclusion of this chapter. Brightes t star Magnitud es . The most impres sive globular cluster in the northern sky "is M1 3 , and in this object the apparent magni tudes of the brightest stars are about 1 2 mag. Not too dissimilar are the bright stars in M92, and , as with all globular clusters , these stars are red giants . I t is only two or thr.ee magni tudes fainter than: the brightest stars that we reach the HR Lyrae variables , so usefal in deriving cluster distances . The magni tudes of cluster stars have of cour se , a direct bearing upon the integrated magnitudes of clusters , and when related to concentration class have a determining effect up on the visual appearance of a cluster , whether any resolution is obtained or not . •

=

=

I

For many clusters the mean apparent B magnitud of the 25 brightes t stars are availabl e , and a wide range ofesfigures are to be foand . At the upper end of the scale the mean magnitude of the 25 brighte st stars in M22' is B 1 3 . 03; at the lower end of the scale we find B 1 7 . 5 1 for N, G C 7006 . Al though the brightes t. s tarS are therefore very faint in the latter objec.t , its concent ration of I enables it to be seen in amateur telescopes , alth oU gh . �tlal� Ss not resolvable in the larger instruments , such as a 1.6�_in c!l· l 2.. Non... Intrin sic Factor s:. Galactic Obscuration. Large numbers of dark nebulae are to be found plotted on the =

=

t

39

Coeli . These , however , are only the most charts of Atlas be realised that the. actual must it d an es ampl eX 'obscuring material in th. e Ga1 ary lS by. no . means. tion of diB tri1:JU d evenly-bordered as; the Coell charts would l ndlcate:. d an sm of the way in which these as U y n t intended to be a critici s method would be equally other any s ted, depic Thi ie � e are' dark n �:a�le, but it i's necessary to state that obscuratio n is 1_pr aat irregular thing. For example, over large areas of t he a pat obY � Coe U shows no dark nebulae abs
.•

•

40

O b s ervat i on o f Gl o bular Clu s ters .

O b s:ervati on o f Globul ar Clus ters .

to obs ervers in northern Europe wi l l no t do so for o b s ervers s l' t e in more southerly l ati tud e s o f the northern hemi sphere In many d c a s e s th l' S l S s o , and c lu s t e r s such a& M4 wi l l appear virtual l e qual o f M 5 or � 1 3 when o b s erve d , f o r exampl e , from the south e n par t s of the Unl t e d state s . H owever , n o t all clu s t e r s wi l l re S p nd to o b s ervati ons made from the l at t e r p ar t s of the world even e w ' � the l arger amat eur t e l e s c o p e s are utili s e d . For example obse made from southern Cal i fo rni a wi th a 1 6t-inch refl e c tor ' have t o achi eve much r e s o luti on on c ertain c lu s ters . Two o f the se a l ed NGC 6 1 44 and NGC 6 2 3 5 ; the respec tive magni tud e s are V 9 . 07 d V = 1 0 . 2 3 , and b o th c l� s t ers l i e in regi ons where the ab sorpt i , of the o rder o f 1 magnl tude . The mean magni tude of the 2 5 bri ght s t �rs in NGC 6 1 44 i s B = 1 6 . 04 , and in NGC 6 2 3 5 i s B 1 6 . 5 6 , an�st thl S , re gardl e s s of the l o o s e s t ruc ture of the s e c lu s ters ( c la ss e s XI aI'lld X respec tively) exp l ains the obtained resul t s .

,

•

=

=

; the � �V�t ;� l oni � la

Two further c lu s t e r s o f intere s t , are M 6 9 and M70 , both of cl a s s V and s eparated by about 2 d e gr e e s ln the sky . 8-inch observat i o n made from Bri t ai n have fully r e s o lved M69 but only r e s o lved the S outer p ar t s of M7 0 ' , M69 i s the nearer o f the two , and i s more affe c t e d by ab sorp tl 0n , by almo s t a magni tude in. fac t . The l ack of f� l l r e s o lut�on � hown by M70 mus t therefore be due t o i t s gr eater dl s t anc.€ ! Whl Ch 1 � over twi c e that of M6 9 . Thi s would have the effect of : educ lng the S l z e of the c lu s ter , making the angular separation of 1 t s s t ars smal l er and the i nner regi on s more c ompre s s ed and hence more difficul t to r e s olve . I t i s of intere s t to no t e that al though 0 the s e two c lu s t ers have a decl i nation o f _ 3 0 whi ch adversely affe c t � d th � o b s ervati o x: s , a 6-inch re frac tor" in the s outhern part o f C al l fornl a produced lden t l, c al resul t s to the 8-inch re frac tor .

NGC 241 9 and the P al omar Clu s t er s . , I t i s n o t onl � c lu s t e r s s i tuat ed toward s the gal ac t i c c entre Whl C h c an show 1 1 t t.l e o r no r e s o lution ; o thers at hi gher gal ac tic l ati tude. s c an b e j u s t as di ffi cul t to r e s o lve o f t en even more so , in fac.t , �d th � prime fac t o : i n the cont ext � f vi s i b i l i ty of such c.lus ters 1 8 thelr concentratl on c l as s . We s hal l bypas s c luster s such as NGC 6 2 2� ( z + 1 3 . 9 ; di s t anc e 2 1 . 6 kpc ) i t s e l f no t at al l a r e s o lvab l e o b J e c t , and t ake NGC 2 4 1 9 ( z = +2 5 . 9 ; di s t ance 6 1 kpc ) as an o b j e c t to c ompare wi th s e l e c t ed P al omar clus t er s . =

N,GC 2 4 1 9 i s o f t en thought by many amateurs t o be the mo s t di s tan.t gl obular c.lu s t e r in the Gal axy . There are however a few wi th greater di s t anc e s , inc luding P al omar :3 , P alo�ar 4 and th.e colus te r di s c overed in 1 97 6 , GCl 0422,.. 2 .1 3 . �he term ' �nt � rgal ac t i c tramp ' has been appl i e d t o N.GC 2 4 1 9 . I t l S n o t a dl ffl cul t o b j e c t t o o b s erve wi th moderate t e l e scop es , i t s c oncen trat i on c l a s s of 1 1 enabl ing i t t o be s e en relativel y easily . The i ndivi dual s t ar s are no t , however , r e s o lvabl e , not . even the brl, ghte s t one s , as they have a mean apparent. magni tud e o � B = 1 8 . 3 � . I t i s ins truc tive to s e e how thi s c lu s t e r c ompar e s wl th some of tho s e o ther remo t e clusters di s c overed on the P al om at Sky Survey p l at e s .

41

an at l e as t be s e en l arge d i s t ance of 6 1 kpc N.GC 2 4 1 9 c t t he u to i t s c oncent ration ely l o s e s , and thi s is due A at e r t e l e s c opn ) i s at the s ame 4 1 omar al P ( ter s lu c Bergh t de / �i h affiT h e Ar p van in many of the s e nt c �as S ' c e and shows the l o o s e s tructu re inhere , c lu s t ers are omar al P e h t f o s tude magni Th e integra ted re , the therefo , f I . 9 1 4 2 NGC than obJ e fainter s gni m tude t 4 a were s r e t s lu c alomar P the alrnOc Sn tr atio n c l as s e s of s ome of l i ght c on ' c al to that of N GC 2 4 1 9 , they would be wi thin the r, l of the l arger amateu r t e l e scop e s . Re s o lution woul d , howeve ers t s lu omar c al P the in s tar s t s e ght bri the as , e b e imp o s sibl 4 omar al P mag for 5 . 7 1 from g are very faint , rangin � e re kn20own) fo r 0 th er s . g ma ver to o e avai l abl e , gone into the fac t o r s relatin g W� have , in the glspac o bular c lu s t ers at some l ength , and in the n of t o bs ervatio the time upon obj e c t s for whi oh r e s o lu t i on of dwel t much c o ess tal ly impo s s ible . Lack of res olution i s n o t o t or l partia er s ei th s , however , many being r e s o lvab l e righ t luster c many conf ine d to too c t s of l o o s e s tructure in densely e j b o ome s Even . e centr the to al ly r e s o lvabl e , M 5 6 , class X , arti p eing b s d l e fi populat ed star affec ted by over 1 magni tude o f ab sorpti on , being typi c al .

dl� t �S ' iden� gr��i (! � I

and

As

far as gl o bul ar c lu s t e r s in external gal axi e s are c oncerned , hemi sphere .o b s ervers have three c lu s t ers in the Fornax thern nor dwarf ga.l axy avai l ab l e , al though from Bri t ai n at l e as t they wi l l present problems due t o their l ow decl ination . Detai l s o f the s e can be found i n t h e l i s t o f addi t i onal gl obular clus t er s , plus details of a no t-to o-faint gl o bular clu s t er as s o c i at e d wi th one of the gal axi e s in the Virgo Clu s t er . For o b s erver s in the southern hemi sphere there are many c .l us t e r s in the Mage l l ani c Clouds , but the s e l i e out side the scope of thi s Handbook .

To a certain exten t explanati ons of the r e sul t s o b t ained by v �ual observati ons c am. be unc ertain ; o b s ervations of a given �i Jghe Clt by the s am e 0 b s e :ver and t � l e sc o p e on two consecu ti ve ts can produc e c.onsl derably dl fferent r e sul t s . Nonethe l e s s , excursion s into the su.b j e c t are always o f intere s t, .

�

Whi le �lo�.ul ar c lu s ters d o n o t pre s ent the vari ety o f form a:ha.J!

ac t 7 rl s h c of o p en c lu s t ers , they are , neverthel e s s , obj e c t s of s t�On � lde rabl e intere s t , and the di s tri bution o f the bri ghter ful.ly r e s o lvab l e c lu s t e.r s wi l l o ften show s truc ture that diep t Infro m the t o t al image s as depi c t ed on pho t o graphs t aken S � th I arge tel e s c ope s . Final ly , t o c l o s e , Fi gure s 1 0 am.'d 1 1 o Ve r l � � af s h ow the s t ar di s tribution in the c lu s ters P al omar 4 t re cen tly di s c overed c lu s t er GCl 042�-2.1 3 , depic ting the gre at �l, f fer e that exi s ts be twe en thi s type of c lu s t e r and Obje c t S such enc as M2 and M 1 3 .

�

42

PART

O b s ervati on o f Globular Clus ters .

THREE

43

A CATALOGUE OF OPEN. CLUSTERS ,

ON �O DUCTI contains observati ons of 2 05 open clu s t ers made:· � o at alo gue b s ervers using t e l e s c o p e s o f 60 t o ,-inches aperture. and bY 1 2 0 x 50 , 1 0 x 50 and 7 x 3 5 binocul ar s . The o b s ervati ons 15 in t o two s e c ti on s c ompri sing a ) descrip t i on s and are d drawi ngs o f 1 76 clus ters and b ) descriptions o f a furthe r !i e u s t er s for whi cb no fi e l d drawings are avai l able .. Di s tri bution 29 ta wi thin the c at alogue is as follows .•

"

.

' .•

.. .

. •

•

,.. .". :

.

eo •

.

.

•

'..

of

�8� �divIde d �

d

a

•

l eft s i d e s of the l eft-hand p age s show the Webb Th e extr eme number (WS ) , the s e continuing in numeri c al al o gue cat ie ty So cu enc� from the l a s t catal o gue entry in Vo lume 2 of the seri e s S Handboo kS . Each Webb Soci e ty number i s f o l l owed by the ac;t ual si gnati on of the c;t.u s t er whi l e for tho s e clus ters whi ch are obj e c t s the M e s sier number wi l l �ppear .below the relevant number . lC or BOO

� � M:s si er

'

Fi gure 1 0 . s tar di s tri bu t i on in the glo bular clus t e:L' P al omar 4 .

The remaining dat a , covering the greater p arts of the left­ pages , is as fo l lows .

hand

Uppel! Line . ( a) p ositions for 1 97 5 . 0

(b) (c) (d) (e )

•

•

•

•

,

•

.'

•

.

•

.'

Trumpler type of c'lus t ers

iln.

the globular

•

•

The abbrevi at ed form of the rel evant con s t el l ation .

The data in ( a) t o ( e ) i s t aken from the. C atal o gue o f Star Clus ters , Asso ci at i ons and Groups ( Al t er et aI , 1 97 0 ) b. a number of c as es addi t i onal informati on wi l l be found be low the data displayed on the upper l ina of e ach entry •

•

Obs erva tions

•

The data below the dotted lines are , in many cas e s , c ontrac ted. enderings o f o b s e:L'vat i ons from the Webb Soci e ty fi l e s . The e vati ons are s e t out in order o f decreasing aperture , the r r a gur. es in parenthesi s , ( 1 2 ) ( 8�) e tc . , are the respec tive. r ure s in inche s . All quo t e d magni tud e s , diameters e t c . are p e eye es timat e s . Where o b s ervations made by more than one per Y hal' s on U sing identi cal t e l e s c o p e s are c onc erne d , the r e sul t s e b e en run t o ge ther into a s ingl e s e c t i o n .

� � �i

Fi e ld

20" Fi gure 1 1 . 1hri ght e s .t s t ar. s clus.ter GCl 0422�21 3 .

mgular di ameters of clus t e.rs in arcminu t e s

Usual

.'

:

M agni tudes o f c,l us t ers;.

�Dr awings-e Th e s e wi ob found on the opposi t e p age s t o the rel evant 8erVat �· onls l, be and consequently number four to a page . All the �a1fi ngs are shown in circl es of 57 mm di amet,er , re gardl e s s of th e �. ctu a � fi eld di ame ters in arcminut e s . In some ins t ances only , � e d� ate are a of a clu s t er i s shown , and for the s e c as e s i n arcminu t e s i s shown under the drawing. In a very few

�

44

A Catal o gue of Open Clus ters .

A Catal o gue o f Op en Clu s t ers .

c a s e s no s c al e i s avai l abl e .

L i s t of Obs erver s .

The f o l l owing l i s t gi ves the names of the o b s ervers who s e wo app e ar s in the c at al o gue . D e t ai l s are al s o shown re garding the �k t e l e s c o p e s used as well as the l o c ations of the se�

D . A . AlIen

M . J . Thorn son D .. Arnbr o s i S . Selleck G .. Hur s t S . J . Hyne s C . Nug.ent E . S . Earker P . Erennan K . Glyn J on e s K . s turdy D . Eranche t t

Eino cul ars D . A . All en K . Glyn J ones D . Eranche tt

6 0-inch 20 12 1 ,* 8 o . g. 1 6� 10 1 0 . 8 , 6 o . g. 10 8�

M ount Wi l s on , U . S . A . 11 Pasadena , C ambri dge , U . K . Minneapo l i s , U . S . A. Cambri dge , U . K . Santa Earbara, U . S . A. Re gina, C anada . Santa BCl,rbar a . U . S . A. Earl s Ear t on , U . K. Wi s taston, U . K . U p ton, U . K . Herne Bay , U . K . Regina, C anada. Winkfi e l d , U . K . 11 Helrns l ey , Ei shop s t o ke , 11

�t

8, 6 8 6 3 7 x 35 8 x 50 15 x 80, 20

x

50

Obs ervers and Accredi ted Clu s t ers .

The f o l lowing l i s t shows al l the open clusters that appear the fi r s t s e c t i on of the c at al o gue ( wi th field drawings ) plus ini ti al s of the r e spec tive o b s ervers . Clu s ters are l i s t ed in c at al o gue order , i . e . , in order of RA .

NGC K NGC Ee NGC K N GC

Tr

1 29 14 1 89 3 1 88 225 16 381 433 436 457 559 581 1

ESB , DAA , DE . GH . GH , PR, DE . GH. DAA, KGJ , DR. GH , SS , DAA . GR. GH , S S , DE . PE. S S , P E , DB . GH , DAA , KS , DB . PE. KGJ . GH.

, GH , ESB , DE . 1 5 0 2 DAA KGJ , P E , DE . , DAA 1 51 ) � SJR, PE. H , G 1 526 DB . GH, 5 1 54 1 5 8 2 PE , DE . DE . 1 6 47 DAA , GR , 1 6 64 GH , P E . 1 7 7 8 GH , P E , DE . 1 8 07 DAA , KS , DE . 1 81 7 DAA , GH , KGJ , KS . 1 8 57 GH . 1 8 93 DAA , GH. 1 9 07 GH , PE. 1 9 1 2 KGJ , KS . 1 98 1 GH , DE . 1 9 60 KGJ , DAA , KS . 2 099 KGJ , DAA, KS . 2 1 29 GH , PE, KS . 2 1 4 1 DAA , KS . GIlL, KS . l e 2 1 56 DAA , GH , P E., KS . NGC 21 58 21 69 SJH, KGJ , KS . 2 1 68 DAA , KGJ , KS . 2 1 74 GH , P E . 2 1 9 4 DAA , KS . 2 1 92 DAA , PE . 2204 PE,. 2 2 1 5 DAA , P E , DE . 2232 DAA, KS , DR. 2244 DAA , GH , ESB, KS . 2251 DAA , GH . . 22 54 GH . 2 2 59 DAA , DAA , P B . 2 264 DAA , DAA , ES B . 2 26 6 PB , DB . 2 287 DAA , KGJ KS . , 22 8 6 PB , DB . 2 2 8 1 DAA, GR, KGJ . 23 0 1 KGJ , PE. 23 0 2 GIll. 23 04 PB . 23 0 9 Gli . !tu. 23 1 1 PB,. P Nce 2 8 GH . 3 2 3 DAA 2 3 2 4 P , KGJ , KS B. � 2 33 5 DAA , PE . liQc 4 6 6 GH . 2 3 43 D AA , GH , KS . 2 34 5 DAA , PE . GC

NGC

654 659 663 7 52 744 869 884 9 57 Tr 2 NGC 1 0 3 9 1 02 7 1 22 0 1 ?45 M 45

J

SH , P B , KS . GH , P E , DE. P B , DE . SJH , KGJ , DB . GH . DAA , ESE, KGJ .

S S , P B , DB . PE . KGJ , DE . S S , DAA , DE . DAA, PE , DB . SS, PE. ESE , KGJ .

in the

NGC 2 3 5 3- DAA, GH , P E . 2 3 5 5 DAA, SJR, DE . 2 3 6 0 DAA, KGJ , PE. 2 3 6 2 DAA, PE , KS , DE . 2 3 67 P E . 2 3 68 PE . 2 3 8 3 PE . 2 4 0 1 PE . 2 4 1 4 PE . 2 4 2 2 DAA , KGJ , S S . 2 4 2 3 DAA , PE . M 7 1 DA , PB. NGC 2 4 3 2 PE, . 2 4 3 9 DAA , DB. 2 4 3 7 DAA , KGJ , KS , DE . 2 447 DAA , KGJ . 2 4 5 3 DAA , GH . H 1 6 GH . 246 GH . H 18 Tr 9 GH . NGC 2 5 06 DAA , KGJ . 2 5 09 DAA , P E . 2 5 2 7 DAA. 2 5 3 9 DAA , KGJ , P E . 2 548 DAA, KGJ . 2 6 3 2 KGJ , KS . 2 6 8 2 KGJ . 6 4 0 5 KGJ , DAA . 6 47 5 KGJ , D E . 6 4 9 4 DAA , KGJ , DE . 6 5 3 0 KGJ . 6 5 3 1 KGJ , DAA , DB. 6 56 8 KGJ , K S . Tr 3 2 GH . NGC 6 6.0 3 KGJ . 6 6 1 1 KGJ . 6 6 1 3 KGJ , DB 6 6 3 3 ESR, KS . rc 47 2 5 DAA, KGJ , KS . NGC 6 6 4 5 PB . 6 6 4 9 PE, DAA . 6 6 6 4 DAA, P B , D B . 6 6 94 DAA , KGJ , KS . 6 7 04 P B . 6 7 0 5 DAA, KGJ , KS . 6 7 0 9 DAA, KS . 6 7 1 6 DAA, DE . 6 7 3 8 P E , DE . 6 7 5 6 PR.

�

45

47 A Catal o gue o r Open Clus ters . NGC 6 7 9 3 6800 st 1 N GC 6 8 1 1 68 1 5 68 1 9 6823 6830 6834 6866 687 1 lC 1 3 1 1 NGC 6883 6885 Rup 1 7 2 l C 4996 Cr 41 9 5 Dol Cr 421 NGC 6 9 1 0 691 3 69 3'9 6940 Rup 1 7 3 174

GH'. DAA, P B , DB . GH,. DAA, GH , DB . DAA, GH, DB . DAA, GH , KS , DB . DAA , PB , S S . DAA , P B . DAA, GH . GH , SJR , KS . GH, DAA . GH_. DAA , GH , SJTh. GH , DAA . GH . GH , SJR. GH. GH . GR. GH, P B . DAA, KGJ , K S . MJT , S S , KGJ . SJH , ESB , DAA. GH . GH .

Rup 1 7 5 NGC 7 0 6 3 7 08 2 7 08 6 7092 7 1 27 7 1 28 7 1 42 7 1 60 7 2 09 l C 1 434 NGC 7 2 3 5 7 2 43 7245 l C 1 442 NGC 7 2 6 1 7281 7 296 7 380 7510 Mark 50 NGC 7 6 54 7 7 88 7789 7 7 90

GB:. GH , DAA. SJR, KGJ . KGJ . KGJ , DB . DAA , GIr , KS . DAA , SJH . PR. DAA , GR, DAA, KS . DAA , ESB , KGJ , KS. GB . DAA, SJH , KS . DAA, ESB , DB . DAA , SJH , ESB . GH . DAA , SJH . DAA , GH . DAA , GH , SJH . DAA, GH . DAA , GH , KS . GH . DAA , KGJ , DB . GH , SJH , DB . GH . GH , SJH .

Below are shown the open c lusters for whi ch no drawings are avai l ab le , and whi ch form the s ec ond s e c tion o f the c atal o gue . The format i s i dentic al wi th the preceding li s t . NGC 1 03 DAA . N_GC 2 3 3 1 DAA, P B . 1 3 3 GH , DAA . 2 37 4 DAA , KS . 1 46 GH , DAA . 2 4 2 1 DA. 1 5 ESB , P B . Mel 7 2 DA. Mel NGC 2453 DAA, P B . NGC 9 56 PB. 24 79 DAA , DA. 1 444 DAA , PB . ESB. 2 DAA . Hyades H NGC 6 507 PE. NGC 1 62 4 PB;. H 1 7 46 DAA , GH , DAA . 1 9 DAA . NGC 67 5 5 DAA , KS . 2 1 1 2 PB . 2 0 DAA. H 2 1 26 DAA, P B . 2 1'86 DAA , KS . NGC 7062 SS 2 1 9 2 S S , DAA, PB. 7 2 2 6 PB:. 2 2 50 P B . 7 7 6 2 MJT , P B . 2 2 69 PR.

A Catal o gu e o f Open Clus ters .

p art On e

Desc riptions and Fi e l d Drawings o f 1 7 6 Open Clu s ters .

49

48

ws

1 62

C at NGC 1 2 9

Dec NGC m Type AD Con +60 0 5 00 2 8 . 5 1 0. 0 IV 2 P 1 1 .0 C as Nuc . o f Cas OB4 . Contains C ephei d DL Cas - - - - - - - - - - - - - - - - - ( 8�) Large group wi th pos sible sub-groups to th e s . , fainter members t o the N and W . ( 8 ) 2 0 s tars x50 ; looks like two c lusters ( 2 5 ' fi eld) ( 2 0 x 50 ) Very bri ght and l arge ; eas i ly resol vab le . into s t ar s ; ali gned in a northerly direc tion . �

1 63

1 64

K 14

NGC 1 89

----... III 2 p Ca s Contains about 40 s tars from 1 0 to 1 4 mag. - - - - - - - - - - - - - ( 1 0 ) Ri ch obj e c t in a ri ch fi eld , app earing as a nebul ous patch x40 ; well -compre s s ed , inc luding three doub l e s of 1 2 mag and below; requires HP to resolve; 29 s tars i n 1 0 ' x 6 ' area .

00 3 7 . 3 +60 5 5 11 .1 Related t o Cas OB4

III 2

P

C as

KING 1 4 1 0-inch x8 0

NGC 1 2 9 · 1 0- inch x8 0

10'

G.

G . Hurs t

Hur st

( 1 0 ) Rather obscure and faint c lus t er o f medium s i z e ; fairly ri ch wi th a few bri ght stars set against a background o f s tars o f 1 2 mag and below. ( 8 ) Roundi sh c lus ter about 4' diameter ; moderatel y ri ch , containing about 2 5 s t ars , about 6 being o f 1 0 t o 1 1 mag and the rest much fainter . ( 1 5 x 8 0 ) Bri gh t , large group increasing in si ze wi th averted vi s i on ; s cattered s tars .

-------�

1 6 5 Be 3

Cas 00 3 8 . 2 + 6 1 2 2 IV 2 p 4.0 Contains about 1 80 s tars . - - - - - - - - - - - - - - - - - ( 1 0 ) Glori ous compr e s s ed c luster cons i s ting of s t ar s o f 1 2 mag and below; hardly detec table at LP , an d no t ful l y reso lved at HP , al though superb at x400 s eeing; 1 1 . 5 mag pair on the E edge .

.

�n

go o d

p.

Bl' ennan

NGC 1 89

BERKELEY 3

8-inch x 1 2 5 Fi eld 2 3 '

1 0-inch x 1 2 0 � G . Hurs t

51 50 ViS 1 66

Cat NGC 1 88

Dec RA AD Type 00 4 1 . 9 +85 1 2 18.0 II 2 r Contains s t ar s from 1 0 t o 1 8 mag. - - - - - ( 8 ) Rather sparse cluster in whi ch i t i s di f fi C ' Ul t to determine the borders ; a l arge number of Very faint s t ars form the background ; c an appear as a ri ch group at LP ; bri ghter s t ar s to the south . ( 1 5 x 8 0 ) Bri ght oval group . -

1 67

NGC 2 2 5

-

-

-

-

-

-

-

-

00 42 . 0 +6 1 3 9 12.5 HI 1 p 0 BD+ 6 1 1 54 ( 1 1 . 2 3 mag) on NW edge , i s associated 1I'i� a smal l , bri ght diffu s e nebula . - - - - - - - -

( 1 0 ) Loo s e group at HP ; two doubl e s o f 1 0 and s tars mainly 9 to 1 1 mag; qui t e impr e s sive at about 3 0 s tars . ( 1 0 x 8 0 ) S t and s out wel l in rich fi e l d . 1 68

K 16

00 42 . 1

+64 0 3

K . Glyn

II 3 p Cas - - - - -

-

-

NGC 2 2 5 1 0-inch x 1 2 0

NGC 1 88 ' 8 -inch x40 Fi el d 6 5 '

Fi eld 2 0 '

G. Hurs t

J one s

. .

( 1 0 ) A very c ompac t , smal l , and p o s s i biy elongated c luster; apart from 1 1 mag principal s t ars the remainder very faint , al though some 1 4 mag member3 are vi sible x 1 2 0 ; about 4 ' di am . 1 69

N GC 3 8 1

Cas IH 2 P 0 1 06 . 8 +6 1 2 7 7.0 Nuc . o f Cas OB1 - - ( 1 0 ) Considerab l e haze along a chain o f stars ; a faint triple s t ar just S o f c entre ; aligned N -S . ( 8 ) Up to 2 5 s t ars , 1 2 mag and fainter wi th a f eW bri ghter members ; about 6 ' di am . ( 1 5 x 8 0 ) Very faint , c ompac t group . -

-

-

-

-

-

-

-

-

NGC 3 8 1 6-inch x 6 5 Fi eld 52 '

KING 1 6 1 0-inch x 1 2 0 4'

P . Brennan

53

52 WS 1 70

Cat NGC 433

RA 01 1 3 . 7

m

Dec +60 00

AD 3.4

Type 2 p

III

C on Cas

( 8 ) Easy but very coarse c luster c ons i s ting o f two l ong chains elongated alm o s t N-S ; the eastern o f the s e is the ri cher ; c ontains one 10 mag , s even 1 1 mag and over fifteen 1 2 mag star s ; 7 ' diam .

1 71

NGC 436

� I 3 m Cas - - - - - - - - - ( 1 0 ) Fairly large , compre s s ed group ; s t ars betwe en 9 and 1 2 mag plus a haze o f unres olved members ; x59 appears more dense on the p . end . ( 6 ) Poor c lu s ter containin g about s i x faint stars and o thers fainter ; poor s i gh t in a sparse fi eld . ( 1 5 x 8 0 ) Extends in a N-S direc tion .

01 1 4 . 0

+58 41

9.8

5.0

� .

1 72

NGC 457

01 1 7 . 5

+ 58 1 2

13.0 I 3 r Cas Cas not a member . About 1 00 s t ar s . - - - - - - - - - - - - - - - - - ( 1 0 ) Tri angl e s o f 9 mag s t ar s grouped mainly to the W; stars conc entrated in smal l group s . ( 8 ) 2 5 s tars plus fainter ones in 2 5 ' fi eld . ( 6 ) Fine group o f l arge and smal l s tars ; no sign o f nebul o s i ty formed by unre s olved members ; 1 0 ' di am. ( 1 0 x 5 0 ) Eas i ly resolvabl e and very bri ght ; star s s cat tered and pointing in a northerly direc ti on .

�

NGC 4 3 6

NGC 433 ' 8-in ch x1 2 5 Fi eld 2 2 ' P.

Brennan

6-inch x65 Fi eld 3 0 '

P . Brennan

. . . : .,. ....

--

1 73

NGC 559

0 1 2 7 . 8 +63 1 1 7.5 1 0. 5 Heav.i ly reddened old clus t er .

II 2 m

.. .

. ' . : :. ' , . . I "

'1"

•

C as

e' ( 8 ) Fairly ri ch group o f faint s tars i n a wedge-shap I tol e l ongated 5 ' x 2 ' . 5 in PA 4 5 0 - 2 2 5 0 and wi de st at NW end ; riche s t part precedes a 1 0 and 1 1 mag p ai!; numerous faint s tars , but n o t a first-rate obj e ct ill

NGC 5 5 9 8-inch x1 2 5 Fi eld 2 2 '

NGC 457 8t-in ch x1 02 Fi eld 2 4 '

thi s aperture due to i t s faintne s s . P . Brennan

55 54 WS 1 74

1 75

1 76

Cat NGC 581 M 1 03

Tr 1

NGC 6 54

Dec RA m 01 3 1 . 6 +60 35 6.8 Bri ghtest s tar 9 . 8 mag.

AD 6.5

Type 2 P

III

Con Cas

- - ( 8 ) Not a very impres sive c lus ter , being l o o s e and poor , and appears b e s t at LP ; contains about h al f a do zen s tars o f mag 1 0 and about 2 5 s t ar s of 1 1 to 1 2 magi double s t ar g 1 3 1 marked on chart oppo s i t e; a red s tar li e s near the mi d-point o f the NE side .

---

8.8 0 1 34 . 0 +6 1 09 4.0 I 3 p Cas - - - - - - - - - - - - - - - - - ( 1 0 ) Two 1 0 mag s t ars and one 1 1 mag s e t against a den s e haz e o f unresolved s t ar s ; outer areas begi n t o r e s o lve at x 1 2 0 ; 1 7 stars c ounted .

..

9.5 5.0 II 3 m 0 1 42 . 2 + 6 1 46 Cas Con tains a number of infrared s t ars . Surrounding interstel l ar matter has a mas s of about 1 500 M . - - - - - - - - - - - - - - - - - - - - - - - � ( 1 0 ) Relatively l o o s e group wi th rich part o f unreso lved s tars t owards the N end ; 1 7 s t ars . ( 8 ) Coar s e but qui t e rich i n faint s tars , particularly

Trumpler 1 8-�- inch x 1 54

NGC 5 8 1 - " M 1 0 3 8-inch x 1 00 Field 4 0 ' K.

Glyn J ones

Fi eld 1 0 '

S . J . Hyn e s

the main portion o f about 3 ' x 1 ' . 5 ; ten 1 1 mag and ten 1 2 mag s tars plus many fainter one s . ( 6 ) Smal l , nebul ous c luster o f 1 2 mag s t ars . 1 77

NGC 6 5 9

01 42 . 5 +60 3 5 9.8 5.0 Contains s tars o f 1 0 to 1 4 mag.

III

-

1 p

Cas -

- -

( 1 0 ) Compac t ; haze o f unr e s olved stars ; c l o s e doubl e o f 1 1 mag wi th a p o s sible 3rd s t ar invo lved ; 1 0 st ars. ( 8 ) Fainte s t part to W; maj ority o f s tars are o f 1 2 mag and below; 6 mag 44 Cas l i e s c l o s e S . p . ( 1 5 x 80 ) Faint , rich large o val .

NGe 6 59 8-inch x1 2 5 Fi eld 2 2 '

NGC 6 5 4 8-inch x1 2 5 Fi eld 2 2 '

P . Brennan

WS 178

Cat NGC 663

RA 01 44 . 3

])ec +61 07

m

7.1

A]) 12.5

Type 2 m

III

Con C as

;

( 8 ) Main body qui te ri ch and two c entral ly s i tu at e par t s very rich indeed' , espec i ally in faint s t ar s . r central regi on 8 ' to 1 0 ' and contains about s i x 1 0 mag s t ars including the c l o s e pair ;E, 1 5 3 , p l u s t e n 1 1 mag s tars and at least fifty 1 2 mag one s ; a m o re or l e s s roundi sh shape i s formed by outliers . ( 2 0 x 50) Large , very ri ch , irregul ar . 1 79

NGC 7 52

1 80 NGC 7 44

0 1 56 . 3

+37 3 3

45.0

III 1 m

And

-

- - - ( 8�) Irregul ar di s tri bution ; bri ghte s t members about 8 mag, the remainder averaging 1 0 mag; orange star on the S edge ; about 50 s tars . ( 8 ) A very fine c luster c ontaining many s tars in p airs ; fi l l s a 6 5 ' fi e l d . ( 1 0 x 5 0 ) Bri ght , rich , scattere d ; easily resolved . IV 2 p 8.6 0 1 56 . 9 + 5 5 2 1 Contains s t ars o f 1 0 mag and below.

'

NGC 663

P.

NGC 7 52

8-inch x7 5

8-inch x40

Field 3 1 '

Fi eld 6 5 '

Brennan

K . Glyn J ones

Per

( 1 0 ) Large , fairly bri ght and compac t ; about 35 s t ars from 1 0 to 1 3 mag; some pairs , the se appe ar ing m o s t noti c eabl e on the SE s ide . 1 81

NGC 869 NGC 8 84

-

P er I 3 r 30 . 0 4.1 02 1 7 . 3 +57 02 Per I 3 r 30 . 0 4.7 02 2 0 . 7 +57 00 Related to Per OB1 . Cephei d s UY , VY , VX Per and SZ Cas are members . NGC 884 i s s l i ghtly olde -r . - - - - - - - - - - - - Obs erved by many , and a s tri king s i ght even i n the smaller tele scope s ; 869 more c ompac t wi th a v erY bright c entre ; up to 2 7 0 s tars in both groupS whl' cb have c l o s e groupings o f red and blue s tars a t the ll

e respec tive c entres ; a red s t ar l i e s halfway be twe the clusters ; both are easy naked-eye obj ec t S .

NGC 744 8�-in ch x1 1 6 Fi eld 2 0 ' llY'n e s

NGC 869

&

NGC 884

8-inch x40 Fi eld 6 5 '

K . Glyn J ones

58 WS 1 82

Cat NGC 9 5 7

Tr 2

1 84

1 85

NGC 1 03 9 Ji13 4

NGC 1 02 7

RA

02 3 1 . 8

AD

Dec +57 2 5

1 1 .0

Co n

Type 2 p

III

P e!'

- ( 1 0 ) Pretty large , bri ght and compact ; well-re s ol ' into s tars o f 1 1 to 1 3 mag wi th a haze of unre s o 'Yed l"v d e member s ; about 44 s t ars at x44 . ( 6 ) Coar s e group of faint s tars e longated E-W; evenly di s tributed in area about 1 0 ' x 4 ' . ( 2 0 x 5 0 ) Faint , small elusive o b j e c t . 20.0 I II 2 p - - - - - - - - - - - - - .. " ( 6 ) x6 5 a brigh t , moderate ly rich clump o f 9 m ag and fainter s t ar s ; main body about 1 5 ' x 5 ' ; about 30 st1,t t o 1 1 mag; s ome faint s t ars to the S . 02' 3 5 . 3

+ 5 5 52

6.9

30.0 6.0 +42 40 II 3 m Per - - - - - - - - - - - - - - - ,- - ( 8 ) Large , bri gh t c luster with three di s tinc tive curved arms o f s t ars radiating from the centre ; IDMy s tars di s tributed in p ai rs , including O� 44 n e ar the c lus ter c entre ; naked-eye obj e c t in a good sky. ( 1 0 x 5 0 ) Large , s c at tered ; easily r e s olvabl e .

NGC , 9 57 a-inch x1 2 5

6-inch x65

Fi eld 37 '

Fi eld 4 5 '

TRUMPLER 2

02 40 . 4

Cas 20.0 III 2 p 0 2 40 . 7 + 6 1 2 6 Regi ons of nebulo si ty l i e in the c luster area . -

-

-

-

- .'

( 1 0 ) Large , l o o s e clus ter , very s c at tered i n i t s appearance ; s t ar s o f about 1 1 t o 1 2 mag wi t h on e s tar a li t t l e bri ghter ; x44 about 4 5 s tars seen pluS a haze o f unres olved members . ( 8 ) 1 5 s tars s e en in a 1 5 ' are a . tbe ( 2 0 x 5 0 ) Bri gh t , ri ch and large ; resolvab l e W ��

th

s t ar s scat tered in i rregular fashi on .

P.

Brennan

P . Brennan

'.

. . .' �

"

OE lt-t,.,

N GC 1 03 9 - M34 8-inch x40 Fi e l d 6 5 '

NGC 1 02 7 6-inch x 6 5 Fi eld 3 0 '

P . Brennan

61 60 WS 1 86

Cat NGC 1 2 20

Dec +53 1 5

RA 03 09 . 8

AD

m 1 1 .8

Type II 2 p

1 .6

(8) (6)

- -

Con Per -

1 0 ' diame ter ; unresolved . Smal l , faint clus ter requiring averted vi s i on . I in superi or transparency shows as a nebulou s p a tch wi th a very few faint st ars s c at tered acro s s . 1 5 x 80 Very faint , opaque haz e .

(

1 87

NGC 1 2 45

)

:----

III 1 r 10.0 9.0 03 1 2 . 9 +47 09 Pe The Per moving c luster Mel 20 i s centred near thi s clus ter at 03h 2 0 3 +48 0 3 1 ' 1 97 5 . - - - - - - - - 1 0 x44 pre tty l arge , compact , ci rcular ; star s o f 1 2 mag and fainter ; x 1 48 resolved into about 1 00 stars but st i l l appears rather hazy . 6 Even di stributi on of 1 1 mag and fainter stars ; x35 qui t e nebulous but resolved x6 5 ; 7 ' di am. -

-

( )

�

(

-

-

-

) (

-

)

-

-

-

( )

1 88

Pl eiades M45

03 48 . 6

+24 01

1.5

82 . 5

I 3 r

NGC 1 22 0 6-inch x 6 5 Fi eld 3 0 '

.

P.

NGC 1 502

K . Glyn J ones

Tau

Many observations were made of thi s clus ter , for which a l arge fi eld o f vi ew i s pre ferabl e ; excellent views were obtained wi th t e l e scope finders and binoculars ; a fi eld o f about 50 t o 60 ' , however , s t i l l r e v e al s an impr e s sive spectac l e ; the refl ection nebula i nc lude s re! NGC 1 43 5 and I C 349 , and may be s een in small ap e r tu 04 05 . 2

+62 1 5

6.0

II 3 p

'.

•

-

-

1 5 st ars in 8 ' area; bri gh t . Tri angle o f s tars o f fairly high magnitud e s ; a well-defined obj e c t in a barren fi e l d . Maj or axi s E-W; 7 mag pair a t c entre ; a

s triking group at all powers . 1 0 x 50 Bri ght obj e c t showing re soluti on .

(

)

.'

Cam

(12) ( 10)

( 8�)

Fi eld 4 0 '

Brennan

--------�

1 89

NGC 1 245 8-inch x1 00

v e rY

-

is

PLEIADES 8-inch x40

NGC 1 502 6-inch x 1 0 5

Fi eld 6 5 '

Fi e ld 2 6 '

P . Brennan

62

WS 1 90

63

Cat NGC 1 5 1 3

RA 04 08 . 2

Dec +49 27

: ':

p o s s b y_ p�r

�

m 9.0

� f_ a_ t �i � l �

AD 9.0

group

Type

II 1 m

Con

�i �h_N�C_ 1 � 2 �

P e!,

� �54i.

" ( 8 ) Poor o b j e c t in a refrac tor , only 1 0 to 1 5 a t at's. i n refl e c tors at x40 small and faint wi th abou t 6 I 1 0 mag s t ars and s ome fain t e r ; c lu s t e r elon gat ed I' n NW-SE line ; about 8 ' x 6 ' di ame t e r . ( 2 0 x 5 0 ) Bri ght , fuzzy group .

1 91

NGC 1 52 8

04 1 3 . 5

+51 1 1

II 2 m .

About SO s tars are known members o f thi s c lus t e r . - - - - - - - - - - -

-

-

-

NGC 1 5 1 3 '

- - -.

8-inch x 1 00

( 1 0 ) Bri ghte s t members on the W edge ; fine s tar patt e rn s wi th a group o f 4 near the c entre ; about

K. Glyn

( S ) Moderat ely r i ch ; about 4 2 s t ar s a t xSO . 1 92

NGC 1 54 5

04 1 9 . 0 -

-

+50 1 2 7.6 - - - - - -

- -

1 5.0 II 2 p - - - -

---

-

-

St-inch x77 Fi eld 3 0 '

Fi eld 40 '

50 s tars s e en in a 2 0 ' are a .

( S� ) Contains many faint s t ar s in smal l group s .

NGC 1 52 S

S . J . Hyn e s

J ones

Per

- - - -.

( 1 0 ) A tri angle o f one 8 mag and two 9 mag s tars

the c lu s ter c entre ; a doub l e o f 9 and 1 1 mag lie

the N edge ; chains o f faint s t ars trai l from the

at

on

c en tre ; 2 3 s tars in a 1 2 ' are a .

( 1 5 x S O ) Fain t , l arge , ri ch o b j e c t .

1 93

NGC 1 5S 2

04 3 0 . 4

+43 4S

30. 0

IV 2 p

An d

About 6 0 s t ar s are known members o f thi s c lu s te r . - - - - - - - - ( 6 ) Con tains about fifteen 1 1 mag s t ar s in a 1 0 '

-

-

are a ; a round , c oars e , poor group surrounded

fairly bri ght s t ar s .

---

b y s ome

( 1 5 x S O ) Bri gh t , l arge and s c at tere d ; resol vab le .

NGC 1 58 2

NGC 1 54 5

1 0- inch xSO L

6-inch x 6 5 Fi eld 44 '

12'

P . Brennan

65 ws

1 94

Cat NGC 1 647

RA Dec m AD Type Con 04 44 . 7 +1 9 02 6.1 35. 0 11 2 m Tau. Thi s c luster i s obscured by 1 . 1 7 magni tude s . ( 1 2 ) 60 s tars s e en in a 2 5 ' are a at x80 . ( 1 0 ) Lo ose group spread over a LP fi e l d ; rich in bri ght and faint doubl es inc luding a 9 mag wi th a n 1 1 mag c ompani on and a 1 2 mag pair in the N p ar t ; 5 3 stars seen a t x80 . -

-

-

-

-

-

-

-

-

-

-

-

-

-

( 2 0 x 5 0 ) Bri ght , ri ch, scat tered obj e c t . 1 95

NGe 1 664

04 49 . 2

+43 40

8.4

12.0

III 1

p

Aur

---.... -

-

.

( 1 0 ) 7 mag s t ar on the E edge ; curving lines of s tars run from the SSW to the NNE ; rich c entre wi th a h aze of unresolved members ; faint but striking; 41 stars . ( 8 ) Many doubl e and tri p l e stars and faint chains . ( 1 5 x 8 0 ) Bri ght , l arge , ri ch ; resolvable except at the c entre where the stars are t i ghtly grouped. 1 96

NGe 1 7 78

05 06 . 4

6.0

+37 01

III

K.

NGe 1 664

NGe 1 647 8-inch x40

6-inch x65

Field 6 5 '

Fi eld 44 '

Glyn Jones

P . Brennan

Aur

2 p

( 1 0 ) Small group containing several doubles including an equal 1 0 mag pair at the c entre ; 20 stars seen at x 1 2 0 in a 6 ' area. ( 8 ) S i tuated in a rich fi e l d ; about 20 stars of 1 1 mag and below; maj or axi s ali gned N-S . ( 2 0 x 50 ) Bri ght and shows some resoluti on .

-------'-

1 97

NGe 1 8 07

05 09 . 2

+1 6 3 0

8.8

II

2 p

T au

-

( 1 2 ) 1 5 s tars in a 1 0 ' are a at x80 . ( 6 ) Sparse group of 9 mag stars in a cruci form s everal pairs o f stars no ted . ( 1 5 x 8 0 ) Bri ght , rich , s c at t ered c lus t er .

-

-

..

s h ap

e;

NGe 1 807

N Ge 1 77 8 6- inch x40

6-inch x6 5 Fi eld 44 '

Fi eld 8 5 '

P . Brennan

67

66 WS 1 98

Cat NGC 1 8 1 1

RA m Dec AD Type C on 05 1 0 . 6 + 1 6 40 20.0 III 1 m 1.8 T au. Po s sible member o f a mul tiple group wi th NGC 1 8 07 , NGC 2 244 and NGC 2 2 52 . - - ( 1 2 ) Faint at x80 ; 40 s t ars in 2 0 ' are a .

( 1 0 ) R e gular in form and stell ar magni tudes ; a t �77 1 8 s t ars seen. ( 8 ) Requires large fi e l d ; like two clusters wi th a gap between ; many faint field s t ars to the NE . ( 6 ) Rich wi th many 1 1 mag s t ar s ; 1 5 ' diameter . 1 99

NGC 1 857

05 1 8 . 3 +39 20 - - - - - - - - -

8.2

-

-

-

1.0

II

2 m

Au.r - - -

-

( 1 0 ) 7 mag orange s t ar at the clus ter c entre ; rich in s tars o f 1 0 and 1 1 magI 1 1 s t ar s ; diam . l ' .

2 00

NGC 1 89 3

05 2 1 . 0 +33 22 1 2 .0 II 2 m 1.1 The gaseous nebula l C 4 1 0 i s as sociat e d . - - - - - - - - - - - - - - -

Aur -

-

NGC 1 8 5 1

N GC 1 8 1 7 8 -inch x40 Fi eld 6 5 '

-

K . Glyn

Jone s

1 0-inch x1 2 0 7' G. Hurst

- - -

( 1 2 ) x80 3 0 s tars in 1 5 ' area , mos tly around the edge o f the fi eld . ( 1 0 ) Contained wi thin a tri angl e o f 8 mag stars ; very ri ch wi th a haze of unre s olved s tar s ; 22 s t ars observed exc luding the three 8 mag one s . 2 01

N GC 1 907

05 2 6 . 4

+35 1 8

II

1 m

Aur

- - -

( 1 0 ) N ebulous at LP ; two 9 mag s tars on the SE edge ; rich core o f 1 2 mag and fainter s t ars ; 1 6 s tar s s e en . ( 8 ) 1 2 to 1 5 s tars of 1 1 mag and below; nebulous background o f unresolved members ; slightly ext ended

in

a NW- SE line , and lies in the same LP fiel d

as

M38•

NGC 1 907 6-inch x6 5

NGC 1 89 3 1 0- inch x80

Fi eld 3 0 '

P . Brennan

69

68 WS 2 02

Cat NGC 1 91 2 M38

RA 05 2 7 .,0

m AD Type Con 6.7 20.0 III 2 m Aul.' The bri gh t e s t s t ar in thi s c luster i s 9 . 7 mag . -

-

Dec +35 49

-

-

-

-

-

-

-

-

-

-

-

-

-

-

( 8 ) Di s tinc t c ruciform shap e , the longer arm o f th e o 0 cro s s in FA 06 5 -245 ; a c on s iderable concen tr at l' on of faint s t ars li e at the c lus ter centre . ( 6 ) Ri ch c luster ; many 1 0 mag s t ars , pairs and a nebulous haz e of unr e s o lved s t ars . 2 03

NGC 1 98 1

05 2 3 . 0

25.0

-04 2 7

P

III 2

-­

Ori -

-

-

-

( 1 0 ) Several bri ght members and many faint star s 1 2 mag on the W s i de ; 2 0 s tars s een . ( 1 0 x 5 0 ) Large , scattered , resolvable obj ect . 2 04

NGC 1 96 0 M36

05 34 . 5 +34 07 6.1 1 5.0 II 3 m Aur The bri gh t e s t s t ar in thi s c lus ter i s 8 . 7 mag. -

-

-

-

-

-

-

-

_.

_

-

.

-

-

( 8 ) Loo s e , bri ght group containing about 3 5 bright s tars ; contains two curved arms ; one extending to the SW ; den s e centre , including two c l o s e pairs , the mo s t s outherly being L 7 3 7 . ( 6 ) 2 0 ' diam . ; contains many outliers . 2 05

NGC 2 099 M37

05 50 . 7

+32 32

24.0 6.1 II 1 r Contains 1 7 0 s tars bri ghter than 1 3 mag.

NGC 1 9 1 2 - ' M38 8-inc h x1 00 Fi eld 40 '

of

K.

8�-inch x1 54 Fi eld 2 0 '

S . J . Hynes

Glyn J on e s

'I,737

!

Aur

NGC 1 98 1

. ' ,

.'

'.

, . , , '

-

-

( 8 ) Contains hundreds of faint s t ars and a red s t � at the c entre , which i s the bri gh t e s t in the gr OUP ; e the c l o s e s t c oncentration s of faint s t ars are t o th N and W ; brighte s t portion about 2 0 ' di ame ter . ( 6 ) Very c ondensed at the c entre ; the maj ori ty of s tars 1 0 mag and below; haze of unresolved s t ar s .

"

.

.

.

.

.

.

.

'

,

.

. .

. ' ' .

.

.

.

• .

.

. . . . .

NGC 1 960 - M36 8-inch x1 00 Fi eld 40 '

,

.

.

.

-

..

'

.

.

.

'

NGC 2099 - M37 8-inch x1 00 Fi eld 40 '

K. Glyn J ones

..

71

70 WS 2 06

Cat NGC 2 1 2 9

RA 05 59 . 6

Dec +23 1 8

m 6.7

AD

Type Con IH 3 p G em - - - - - , ( 1 0 ) Compac t group wi th faint s t ars grouped ar o 1ln. d a tri angle of 8 and 9 mag one s ; 1 7 s t ars . 5.0

( B ) Irregular form ; s t ars mainly of 1 1 mag an d fainter; s t ands out wel l at MP and HP . ( 6 ) Nebulous c luster o f small s t ars . 2 07

NGC 2 1 41

06 0 1 . 7 +1 0 2 6 1 0. 8 10.0 - - - - - - - - - - - - -

H 3 r - - - - -

---.... Ori - - , .

( 1 2 ) At least 2 0 s t ars in 8' ; no t fully resolved , ( 6 ) Nebulous and very faint ; unresolved ; 5 ' di am , 2 0B

I C 2 1 56 2 1 57

8.5 06 03 . 2 +24 1 2 5.0 06 03 . 3 +24 05 - - - - - - - - - - - - - - - -

IH 2

P

G em

NGC 2 1 41

NGC 2 1 29 ' S!-inch x1 54 Field 1 0 '

-

6-inch x40 Fi eld 7 6 '

-

- - - - -. . ( 1 0 ) Bo th c lusters in s ame fi eld ; bright s t ars are l ac king in bo th , and a background haze evident ; a 9 mag s l i ghtly orange s t ar on the S edge of 2 1 57; 6 s tars in 2 1 56 and 9 s t ars in 2 1 57 .

S.J .

P. Brennan

Hynes

( 6 ) About 2 0 s tars o f 1 0 t o 1 2 mag. 2 09

NGC 2 1 5B

Gem 06 05 . B +24 06 H 3 r 1 1 .6 Bri gh t e s t s tars red gi an t s , wi t.h absolute magni tudes c omparable to the bri gh t e s t s t ars in globul ar clus ters -

- - -

( 1 2 ) xBO i rregular and barely re s o lved . ( 1 0 ) On the SW edge o f M3 5 ; hazy patch at L P; about 1 0 s tars resolved x1 2 0 . ( 8 ) Faint , wi th a few faint s t ars seen; appe ar s as a small , nebulous patch at LP . . g fotJll ( 6 ) Like c ometary nebula at LP ; at HP a curv�n o f faint s t ars extending SW from a brigh ter s t ar .

le

NGC 2 1 5B 6-inch x6 5

2 1 56-7 1 0-inch xBO

Fi eld 48 '

P . Brennan

73

72 WS 210

Cat NGC 2 1 69

RA Dec m Type C on 6.4 06 07 . 0 + 1 3 58 I 3 p Ori Thi s c lu s t er i s obscured by 0 . 1 7 magni tude s . -

-

( 8� ) 1 5 s t ars well di s tributed and showing a b l u i sh tinge ; the brighte s t s t ar , o f 8 mag , l i e s on t h e E N edge of the c lus ter . ( 8 ) Redd i sh s t ar in Nvl corner ; about 8 ' di am . ( 6 ) Small and sparse ; s tars from 1 0 t o 1 2 mag. 21 1

NGC 2 1 68 M3 5

---

6.0

..

29 . 0 IH 2 m Gem C ontains 1 2 0 s tars bri ghter than 1 3 mag. The bri gh t e st s t ar i s a B3 obj ect o f 7 . 5 mag. ( 1 2 ) Very ri ch ; 1 1 0 s tars in 2 5 ' area. +24 2 1

06 07 . 3

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

N GC 2 1 6 9 8�-inch x 1 1 6

-

( 8 ) Contains more than 2 0 8 t o 9 mag s tar s , formi ng deli cate loops and curls , wi th numerou s fainter stars in the background ; a curve to the NE ends in the bri ght s t ar 5 Geminorum , ( 6 mag) .

NGC 2 1 68 - M3 5 8 - inch x40 Fi eld 6 5 '

Field 8 ' S.J.

K.

Hyne s

Glyn J one s

( 6 ) Starl e s s regi on at the c entre ; s t ar s are mainly whi t e , though one yel lowi sh and one greenish seen . 212

NGC 2 1 74 2175

Ori 6.8 06 08 . 3 +20 2 0 1 5.0 IV 3 p Related t o Gem O B.1 . Refl ection nebul a as sociated . ( 1 0 ) Jus t suspec ted x80 as a group o f s tars app earing out of focus ; a smal l circular halo around a fe w s t ars -

-

-

-

c ompri s e s the northern par t . ( 8 ) Spars e ; about 1 5 s tars o f around 1 0 mag.

-----213

NGC 2 1 94

Ori 06 1 2 . 4 + 1 2 50 H 1 r - - - - tile ( 1 4 ) Rich , concentrat ed group ; brighte s t s tar s on E par t ; many unresolved members show as nebu l o si ty . ( 1 2 ) 1 5 s t ars in 5 ' area; many unre s olved memb e r s . ( 6 ) Faint group , 6 ' di am . , composed o f a numb er o f -

-

-

-

-

-

-

-

-

-

-

-

1 2 mag s t ars and unr e s o lved nebulo s i ty-.

-

-

-

-

NGC 2 1 74 -5 1 0-inch x1 2 0 L

NGC 2 1 94 1 0- inch x1 2 0

4'

6'

G . Hur s t

7,4

ws

214

15

C at NGC 2 1 92

RA 06 1 3 . 4

Dec +39 52

m

1 0.9

AD

6.0

Type III 1 P

-

Con Au!' -

( 1 4 ) Faint group in a rich fi e l d ; easy to pa s s OYe l'j no unr e s o lved member s . ( S ) 2 0 faint s t ars in an amorphous group ; 1 0 ' di� . ( 6 ) Smal l , roundi sh , co ar s e clus ter ; about a dO z en very faint s tars acro s s a nebulous background . 215

NGO

2 2 04

06 1 4 . 6

-1 S 39

9.6

12.0

CM a ---""

III 3 m -

..

-

-

( S ) Almo s t invi sible at low magni fication s , but qUi te easy at x 1 2 5 ; the c luster i s c o ars e , and cont ain s 25

NGO

to 30 s t ar s , s ome of 1 1 mag, but mo s t 1 2 mag and fainter ; main body 6 ' x 3 ' , and wi th outli ers this

NGC

2 1 92 ' 6-inch x6 5

S-inch x 1 2 5

Fi eld 41 '

Fi el d 2 1 '

2 2 04

is increased to s ome 1 0 ' . 216

NGO

22 1 5

06 1 9 . 6

-07 1 7

8.6

10.0

II 2 p

P.

Mon

P . Brennan

Brennan

( 1 2 ) 2 0 s tars i n 9 ' are a . ( 6 ) Smal l , co ar s e grouping of faint s t ars ; contains

217

NGC

about 2 0 t o 2 5 s tars o f 1 0 t o 1 1 mag and fainter; there are 2 or 3 s t ar s bri ghter than 1 1 mag, but the c luster s t ands out wel l at x6 5 ; a 7 mag s tar pre cedes. ( 2 0 x 50 ) Large ; tightly grouped toward s the c en tre .

-

2232

06 2 5 . 5

-04 43

4. 3

20.0

IV 3 p

MOD -

- - .

( 1 2 ) 1 5 s t ars in 2 0 ' X 1 0 ' fi eld ; bri ght . ( 6 ) Spar s e c luster around 1 0 Mon ; 5 s t ars se en x6 0 and no increase x1 2 0 . ( 3 ) Brigh t , smal l , tightly grouped at the cent r e ; easily r e so l vable .

NGO

NGC

221 5 6-inch x65

2232 6-inch x6 5

Field 4 1 '

Fi eld 4 1 '

P . Brennan

77

76

WS 218

Cat NGC 2 2 44

RA Dec m AD Type C on 06 3 1 . 8 +04 53 5.3 20.0 II 3 p Mon Related to I'1on OB1 ; c onnec t ed with gas eous n e bu.l a NGC 2 2 3 7 , 2 2 3 8 , 2 2 3 9 , 2 2 46 , the Ro s e t t e Nebu l a . - - - - . ( 1 2 ) 3 0 s t ars in 2 0 ' area; nebul o s i ty very e Vid e ' nt ( 1 0 ) Large group dominated by 6 mag yellow s t ar 12' Hon ; 2 5 s tars to mag 1 2 . ( 8t) Blui sh and whi te s tars barring 1 2 Mon ; NW p a rt devoid of s tars ; very few doubl e s ; s l i ght ind i c atl' on! o f nebul o s i ty in c ertain areas . ( 6 ) Very large clus ter ; no nebulo s i ty seen.

21 9

220

NGC 2 2 5 1

NGC 2 2 54

06 3 3 . 4

+08 23

8.5

III 2

P

--­ - - - .. Hon

( 1 2 ) x80 2 5 s tars in a s treak ; 2 0 ' x 5 ' diamet e r . (J O ) Elongated group extending NIl-SE ; chain o f stars s tretching S c ontains considerable haz e ; 1 9 stars , some reddi sh ; in a rich region . ( 2 0 x 5 0 ) Bright ; c entre parts brigh t e r . 0 6 34 . 7

+ 0 7 42

11 .1

I 2 p

NGC 2 244 ' 8 -inch x40

-

NGC 2 2 5 1 1 0- inch x80

Fi eld 6 5 ' K. Glyn

Jone s

G . Hurs t

Mon

- - - ..

( 1 0 ) Very small , c ompac t group forming a U-shapej 5 s tars s een , o f about 1 1 mag, the s e appearing in a regi on of consi derable haze at x1 2 0 .

--------' f10 n 06 37 . 2 +1 0 5 5 II 2 p 1 0.8 NGC 2 2 59 - - - - -.

221

( 1 2 ) 1 0 s t ars in 5 ' area; ( 8 ) x50 unresolved group 8' acro s s . tei er ( 6 ) Very di ffi cul t , but glimpsed at times wi t h av vi sion; a small e l ongati on about 3 1 x l ' in extent vri th some very faint s t ars scat tered acro s s �, t ,, a

NGC 2 2 54 1 0-inch x 1 2 0

NGC 2 2 5 9 6-inch x6 5

faint s t ar li e s on the N edge ; no t s e en at x3 5 ·

Fi eld 49 1

P . Brennan

79

78 WS 2 22

Cat NGC 2 2 64

Dec RA m AD Type Con 06 3 9 . 8 +09 5 5 4.1 30.0 IV 3 p Mon Related to I'lon OB1 . Thi s c luster i s wi thin an II 11 regi on wi th NGC 2 2 5 9 . H CO , OH and o ther mol e cu.l 2 es are to be found in the associated dark cloud s . - - - - - - - - ( 60 ) The weak nebulo s i ty just S o f 1 5 Mon j us t s e en in a rich fi eld of bri ght s tars . -

-

-

-

�

( 1 2 ) 40 s t ars in the 2 5 ' area around 1 5 Mon . ( a1a - ) Extended almos t parallel t o the galac t ic pl an e., l o o s e di s tribution ; maj o ri ty of s tars 8 to 1 0 mag, 2 23

NGC 2 2 6 6

II 2 m Gem - - - - - - - ( a ) Outliers extend to 4 ' , but the riches t part i s 2 ' in diameter; very ri ch in faint s tars , plus a fev 1 1 mags and a 9 mag on the S edge ; about 3 5 s t ar s at x2 0 5 and 2 0 1 2 and 1 3 mag s tars in the centre . 06 4 1 . 7

NGC 2 2 64 S!';'i nch x 5 1

+2 7 00

�

- .

NGC 2 266 8 - inch x1 2 5

Fi eld 45 ' E.S.

Barker

Fi eld 2 6 '

P . Brennan

( 1 5 x 80 ) Oval ; brighter towards the centre . 224

NGC 2 2 87 M41

CMa II 3 m 0 Neutral hydrogen i s di s tributed up to 1 around this

06 46 . 0

- 2 0 42

5.0

32 . 0

clust er , whi ch has a mas s o f about 600 M ®

• -

-

-

_

.

( 2 0 ) 5 5 s t ars in 1 5 ' ; the bri gh t e s t i s orange . ( 8 ) Roughly circular wi th irregular extension s , these m o s tly to the N ; double s t ar on the W edge . ( 6 ) Contains many 9 to 1 1 mag s tars , the pre domi n�t colours being whi te ; at the c entre 2 8 mag s tar� 225

NGC 2 286

06 46 . 4

- 03 09

8.6

1 3.0

IV 3 m

-

-

( 8 ) Main body ali gned NE- SW; a tri angle of thr e e 9 mag s t ars l i e s on the SE edge ; 3 8 s t ars s e e n . ( 2 0 x 5 0 ) Brigh t , rich an d l arge .

�

NGC 2287 - M41 6 - inch x80 Fi eld 50 '

NGC 2286 6-inch x40 Fi eld 7 6 '

P . Brennan

81

80 ws

226

Cat NGC 2 2 8 1

RA 06 47 . 6

])ec +41 0 5

m 6.7

AD

Type I 2 p

1 0. 0

( 1 2 ) 3 0 bri ght s t ars in an 1 8 ' area . ( 1 0 ) Two very c l o s e doubles a t the c entr e ; ab out 2 5 s t ar s s een wi th fainter one s glimpsed . ( 8 ) Very bri ght c luster wi th a ki te-like shap e ;

den s e s t part l e s s than 2 0 ' di ameter . 227

NGC 2 3 0 1

06 50 . 5

+00 30

15.5 I 3 m Weak H II i s vi sible on the P alomar Sky Survey. - - - - -

-

-

and 2 o f 9 mag on t he SW edge ; a bri gh t c lust er wi th about 50 s tars vi sible . ( 1 0 x 50 ) Bri ght and reso lvable . 228

NGC 2 302

06 50 . 7 (10) is a s ome al s o

229

NGC 2 304

-07 02

2.5

II 2 p

I.

Mon

NGC 2 3 0 1

NGC 2 2 8 1 , 8 -inch x1 00 Fi eld 4 0'

( 8 ) The maj o r axi s i s aligned NE-SW , the S e d ge of the group being concave ; contains 8 s tars of mag a

Gl yn Jones

6-inch x65 Fi eld 4 5 '

P . Brennan

- - - - - - - - - - - - . .1-----+---1

Neat , c ompac t group , be s t s een at x80 ; there bri ght triangl e of s tars near the c entre , plus haz� o f unr e s o lved members ; a few faint doubles no t e d ; 1 3 s tars .

06 5 3 . 6

+ 1 8 03

1 1 .5

3.0

II 1 p

Mon -

-

.

( 8 ) A very ri ch group o f very faint s tars , w�. th only a few being as bri ght as 1 1 mag; the c lus ter �, s about 3 ' x l ' in s i ze , being elongated SW-NE ·, the r i c he st at part form s the maj or axi s ; appears alm o s t ne bu l oUs LP ; averted vi sion advantageous .

NGC 2 3 02 1 0- inch x80

NGC 2 3 04 8-inch x 1 2 5 Fi eld 2 2 '

L P . Brennan

83 82 ws

2 30

Cat NGC 2 3 09

RA 06 54 . 8

Dec -07 1 0

m 1 0. S

AD 3.0

Type 2 m

11

C on Mon -

-

-

( 1 0 ) A very small , ri ch c lus t e r , wi th s tars mainl y of 1 1 to 1 3 mag and below; c ontain s much haz e d 1.l.e to unresolved members , and i s n o t fully res o lved up to x1 2 0 ; a faint double li e s at the c ent r e ; 3 ' diam ; 9 s tars .

231

NGe 2 3 1 1

--..... III 2 p 9.S -04 3 3 Hon - - - - - - ... ( 6 ) A fairly rich clus ter of 1 1 mag s tars abou t 5 1 in di am e t er ; about 2 0 s t ars s e en on a s l i ghtly n ebulous background ; in a rich field .

06 56 . 5

-

232

Rup S

07 00 . 5

-

IV 2 p

-1 3 3 3

-

-

-

CMa -

-

( 1 0 ) Very faint , small and di fficult ; an S mag Md a 9 mag s tar lie at the N end ; no o ther stars in at

the area are bri ghter than 1 2 magi 9 stars seen xSO ; diameter about 6 ' . 2 33

NGe 2 3 2 3 M50

Mon 16.0 II 3 m 07 01 . S -os 1 S Thi s c lus ter contains s tars of 9 mag and below, many being reddened due to obscurati on. - - - - - - - - - - - - - - ( 1 2 ) 1 2 0 s t ars ; circular c entre , S ' in di ame ter , from whi ch s tars spread in curved rays to give -

-

to tal dimensions o f about 2 5 ' x 1 0 ' . ( S ) Appears as a bright , den s e conc entrati on

-

.

-

NGe 2 3 09 .

G.

NGe 2 3 1 1

1 0-inch x 1 2 0

6-inch x6 5

�

Fi eld 42 '

P . Brennan

Hurst

..

in

the Mil ky Way ; rich in groups o f faint s tars , �d ring s tands out well owing to being surrounded by a o f s l i ghtly darker s ky ; red s t ar on SE edge . ' Jl ( 6 ) S tars i n a rough Y�shap e ; s l i ghtly nebul oU s 1 the c entre ; in a rich regLon .

RUPRECHT S 1 0-inch xSO

NGC 2 3 2 3 - M50 8-inch x1 00 Fi eld 40 ' K.

Glyn Jones

85 84 WS 2 34

Cat NGC 2 3 2 4

RA 07 02 . 9

Dec +01 06

m 8.8

AD 9.0

Type Il 2 r -

-

-

,

( 6 ) S i tuated in a very rich fi e l d ; in go od s e e ' lllg shows as a carpet of very faint stars , rich and qui te compre s s e d ; roundi sh shape and about 7 ' Or 8 ' di ame ter; two 9 or 1 0 mag s t ars superimp O s ed , one central , the o ther on the NE edge . 235

NGC 2 3 3 5

� 1 0. 0 III 3 m Mon Nuc . o f CMa 0]1 . Po s sible doubl e wi th NGC 234 3 . 07 0 5 . 4

- 1 0 02

-

-

- ...

( 1 2 ) 2 0 st ar s in 1 5 ' area. ( 8 ) Tri angl e o f two 8 mag and one 9 mag on the SW edge ; trapezium o f 7 mag and 9 mag stars on the N edge ; 1 1 mag s t ars at c entre ; about 30 s tars , 236

C r 466

07 06 . 2

-1 0 40

11 .1

Mon

III 2 p

( 1 0 )Extremely di ffi cult to locate and see ; at LP i t appear s nebulous and at x1 2 0 a few stars are r e so lved , the remainder showing as a nebulous haz e ; no m embers bri ghter than 1 1 mag; diameter about 4 ' ; 7 st ar s s e en . 2 37

NGC 2 343

07 07 . 1

- 1 0 37

6.0

III 3 p

-

-

P. Brennan

6-inch x6 5 Fi eld 42 '

P . ]rennan

-

Mon

-

NGC 2 3 3 5

NGC 2 32 4 , 6-in ch x65 Fi eld 42 '

_

.

( 1 2 ) 1 5 s t ar s in a compact group 5 ' acro s s . ( 1 0 ) Intermedi ate ri chne s s c lus ter ; a comp ac t triangle o f 9 mag s t ars enc lo sing a group of s t ar s o f 1 0 mag and below; di am . 7 ' ; 1 6 st ars . ( 6 ) Tri an gular group ; 3 bri ght s t ars and a feW more fainter one s at x1 2 0 .

COLLINDER 466 1 0-inch x 1 2 0 L

NGC 2343 1 0-inch x 1 2 0

4'

G . Hurs t

87 86 WS 2 38

C at NGC 2 3 4 5

RA

07 07 . 2

Dec -1 3 00

m 8.3

AD 12.0

Type

Con CMa

' ( 1 2 ) 1 2 s tars in 1 0 ' area; more faint one s su s P e c t e, ( 6 ) Fairly ri ch and easy ; contains about 2 0 s t ar s 0'Q, 1 1 mag wi th 5 or 6 s tars o f 9 and 1 0 mag int er s the c lu s t er i s much elongat ed NE-SW, and abou t 1 2 'x in s i z e . -

2 39

NGC 2 3 53

07 1 3 . 5 -1 0 1 5 Related t o CMa OE1 .

II 2 p

Man

- - -

-

NGC 2 34 5 ' 6-inch x65 Fi eld 4 5 '

( 1 2 ) 3 5 s tars spread over a 2 0 ' fi eld . ( 1 0 ) 6 mag s tar at the S edge wi th a 9 mag dou bl e t o the NE ; about 3 0 s tar s . ( S ) 7 mag s t ars at N and S o f the c lu s ter ; curVe of s t ar s from the W to the SW edge ; about 60 s tars inc luding probable field one s . 2 40

NGC 2 3 5 5

Gem II 2 p 9.0 07 1 5 . 6 + 1 3 49 - - - - - - - - - - ( 1 2 ) 2 0 s tars in 6 ' area ; very faint . ( 1 0 ) Rich group , very c ompac t around a 9 mag star ; 1 1 mag doub l e in the NW part ; x 1 2 0 needed to re s o lve member s ; 22 s tar s ; diameter 7 ' . ( 1 5 x S O ) Faint and very ri ch .

P.

Brennan

NGC 2 3 5 3 6-inch x6 5 Fi eld 45 '

P . Erennan

-

:

--------� CM a NGC 2 36 0 -1 5 3 6 II 2 m . -

241

-

- - - - ( 1 2 ) 50 s tars in 1 5 ' are a ; impr e s s ive . ( S ) Compact c lu s ter ; arrow-head shape poin ting t o the E ; 9 mag on E edge and 6 mag s t ar to the W . d olve ( 6 ) Rich , compact group wi th nebulo s i ty of un r e S " s t ar s ; t apering arm o f faint s t ars and nebul oS 1 t y -

points t o the S , ending wi th a bri ghter s tar .

-

-

. : .. .

NGC 2 3 5 5 1 0-inch x1 2 0 7' L

NGC 2 3 6 0 S inch x 1 00 Fi e l d 4 0 ' K.

Glyn Jones

'

'

.

89 88 WS

242

Cat NGC 2362

RA

07 17 .6

Dec -24 55

m 3.9

AD 16.0

Type I 3 p

Con

CMa

Nuc. of Vel OBt; contains about 240 stars. - - - - - - - - - - - - -

-

(10�) 40 stars in 3' area plus outliers.

..

(8) 5 stars of 10 mag and 20 fainter members; the richest concentration surrounding and a little S of tau CMa. (6) Not easily visible at LP due to t au CMa; 15 stars seen including the latter. (3) Tightly grouped at the centre; resolvable. 243

NGC 2367

07 19.1

-21 53

NGC 2362.

NGC 2367

6-inch x105

6-inch x65

Field 26'

Field 30'

-

IV 3 p

7.8

-

CMa -

-

- .

(6) A small, coarse cluster; the 4 brightest stars •

of 10 and 11 mag, are arranged in a Y-shape; the cluster contains about 10 members while fainter

P. Brennan

stars are evident. 244

NGC 2368

07 19.8

-10 20

IV 2 p

11.8

P.

Brennan

Mon

(6) A small, roundish, faint cluster; contains about 10 very faint stars against a background that is slightly nebulous; an 11 mag star lies on the Wedge; 3' diameter. 245

NGC 2383

-20 53

8.8

5.5

-

CMa

I 3 m -

-

-

..

..

arS; (6) Small, faint cluster in a field of faint st

ct; it appears nebulous but is not a difficult obje

the very rich field includes the asterism NGC 2384• shown on the chart opposite. NGC 2368

NGC 2383

6-inch x65

6-inch x65

Field 42'

Field 42'

P.

Brennan

91 90 ws 2 46

Cat NGC 2401

RA

07 28.3

(6)

-

Dec 13 55

A small,

m 12.7

Type

AD

Con Pltp

II 3 p

32.0

'

roundish cluster showing as nebltlo . Sl ty.

shows very little central brightening, and is ab 01lt l' in diameter; situated among many field stars . , 1t

shows no resolution to this aperture. 247

NGC 2414

07 32.1

-15 23

I 3

7.8

'

-­

ID

Pltp

This cluster is situated in outer spiral arm II of the Milky Way. -

(6) A small cluster, 2' in extent, it surrounds a 9 mag star,

elongated W-E',

and with averted v isi on

several very faint stars are seen; 248

30.0

-14 25

.

-

NGC 2414

6-inch x65

6-inch x65

Field 42'

quite rich.

III 2 m

NGC 2401.

Pltp

NGC 2422

07 35.4

M47

The brightest star in this cluster is 5.7 mag (12) 60 stars in 20' area; contains prominent

P.

P. Brennan

Brennan

�--------------------------------�

__

double; t r

________ __ ________________ __ __

(8) Contains relatively few bright stars; two arcs of 3 stars lie to the SW,

Field 42'

and near the centre is Z 1121,

while L 1120 lies on the W edge; naked-eye object. (6) Loose; 249

NGC 2423

07 36.0

rich in bright stars.

-13 48

19.0

-

IV 2 m

Pup -

-

.

(12) 60 faint stars in 20' area. lus ter (6) Contains a 9 mag star slightly W of the c mag centre; the remaining 40 stars are mostly 10

ted and fainter, and are quite rich and distribu d exten evenly; some stars are in pairs and outliers diaJll.; to about 20', although the main body is 10' ies round, or just slightly elongated W-E; M47 l

just outside a 56'

field to the S.

NGC 2422 - M47

NGC 2423

8-inch x100

6-inch x40

Field 40'

Field 56'

P.

Brennan

93

92 WS 250

Cat

Mel 71

RA 0 7 36.5 - - - -

Dec

AD

m

-11 53 9.0 - - - - - - - - -

7.0

'rype

II -

-

1 m -

Con

-

-

PUp

-

-

(10) Round with great central condensation; like a

large, open globular cluster; about 8' diameter . (8) 12 mag and fainter stars distributed across

a

nebulous area; very compressed, and has a round shape with irregular edges; 6' diameter. 251

NGC 2432

07 39.8

-19 02

10.2

II

1 p

-

Pup

- -

-

-

(6) A small, very much elongated group which is

about 3' x l'

in extent; with averted vision it is

resolved into about a dozen 11 mag stars; somewhat

nebulous with direct vision; stands out well. 252

NGC 2439

-31 36 07 40.0 - - - - - - - - - -

-

8.0 11 3 m Pup - - - - - - - - - - - - - -

-

(10t) 15 stars in 4' area; other stars suspected. (3) Bright, rich,

MELOTTE 7�

NGC 2432

6-inch x65

6-inch x65

Field 35'

Field 35'

P. Brennan

P.

Brennan

with stars scattered in the outer

regions; easily resolvable. 253

NGC 2437 M46

07 40.6

-14 44

6.7

24.0

IV

2 m

Pup

Contains a number of extremely bright AO stars; the

planetary nebula NGC 2438 lies on the NE edge. - - - - - - - - - - - - - - - - - - -

-

- -

(12) About 170 stars in a superb field of 23'· (8) A fine sight; about 30'

in diameter and very

rich in faint stars which are condensed in the

central area; the brighter stars stretch away to the N and E, and there is a solitary 8 mag red

star about 20' to the SW; can be very faint in a

sky not completely dark or clear.

of (6) Stars of 8 mag and below; some nebulosity ter unresolved stars following curves of the brigh

NGC 2439

NGC 2437 - M46

6-inch x65

8-inch x100

Field 35'

Field 40'

stars; NGC 2438 seen on the NE border. (3) Rich and scattered; faint stars.

K.

Glyn Jones

95

94 ws

254

Cat NGC 2447 M93

RA

07 43.5

Dec -23 49

m 6.3

AD 16.0

Type

IV 1 P

Con Pu.p

The brightest star in this cluster is 9.7 mag. - -

. . ......,. : .... .

(12) 45 stars in 12' area; faintish. (8) A bright,

. . :eo.:,': e' : ....:. .

,'

fairly condensed cluster, contai ning

20 or more brightish stars and many fainter ones

concentrated towards the centre; the two brigh t est

stars are to the SW, and the brightest members ar e

spread out in straggling arms. 255

NGC 2453

07 46.7

-27 11

I 2 p

8.6

--­ Pu.p

-

-

(10t) 20 stars in 4' area; neat group. (10) Grouped close to a 9 mag star; circular and

about 5' in diameter; inner condensed area in which

5 stars of 10 mag and below are seen.

256

Ha 16

(3) Faint and small; tightly grouped at the centre.

07 49.2

2.0

-25 23

I

1

NGC 2453

NGC 2447 -, M93

- -

K. Glyn

8-inch x100

10-inch x120

Field 40'

5'

Jones

G. Hurst

Pu p

P

(10) Quite a severe test; apparent nebulosity NW of

a 9 mag star; about 2' x 1'.5 and possibly elongated

NE-SW; only 3 stars detected in the nebulosity; � extension of nebulosity possibly seen to the SE.

257

NGC 2467 Ha

18

07 51.4

-26 20

7.2

12.0

imposs.

pup

-

The Related to Pup OB1. Ha 18b and Ha 19 associated.

9.23). nebulosity is excited by HD 64315 ( V - - - - - - - - - - - - - - - - - - =

-

-

�

f bout (10) Apart from 2 stars of 8 mag members are 0 a

e ' 10 mag and below and scattered over a large ar a ,

. IIa nebulous patch just S of the cluster centre �s this is about 1'.5 diameter, and just

S

a 8' 1 ,

of a 10 JIIag

a star; the only star �isible in Ha 18 is an 11 w g

HAFFNER 16

NGC 2467 & HAFFNER 18

lO-inch x120

10-inch x120

10'

one just within the northern part.

G. Hurst

97

96

WS

2 58

Cat Tr 9

RA

07 54.2

( 10 )

Dec

-25 52

m 9.0

AD

Type I

6.0

2 p

- - - - -

-

Co n PUp

The cluster almost fills the field at x1 20.

, it

shows an irregular outline and initially appe ars

rather loose; at HP an inner scattering of fai nt

stars, the brightest being of about 10 mag, with a

heavily condensed region in the

SE

part in wh i ch 2

stars only are visible in nebulosity of 2'

15 stars seen in all. 259

NGC 2506

07 58.9

-10 43

8. 3

er ,

---.. Mon - - - -.

I 2 r

10.0

diame t

TRUMPLER 9

( 12 ) 15 stars barely resolved, others not resolved, ( 8 ) Faint, dusty cluster, about 10' diameter, with

8 to 10 stars of 10 mag and many fainter; not very

impressive 260

NGC 2509

5.0 Il 1 p -19 00 07 59.6 9. 3 Pup - - - - - - - - - - - - - - - - - - - - - - - ---

NGC 2506

10-inch x120

8-inch x100

8'

Field 40'

G. Burst

K.

Glyn Jones

( 12 ) 10 stars only seen, and others suspected. ( 6 ) Faint, roundish, nebulous object with a brighter

centre; well-resolved at the edges and to a lesser

extent in the middle; the cluster stars are very

faint, but stand out well in a rich field; 5' di�,

-

261

NGC 2527

08 04.2

( 10! )

(6)

20'

-28 05

8.0

x140 60 stars in 7'

x 4'

Pup - - -

III 1 p

22.5

group.

A moderately rich but coarse cluster, some X

E-W; the E

15' in extent and elongated

members of 9 and 10 mag lie near

test the bri gh

out edge; ab

' e half the members are fainter than 11 mag", a l �n

3 mag 8 and mag 9 stars, 8' long lie 15'

in identification.

SE ,

of

d a.id an

NGC 2509

NGC 2527

6-inch x65

6-inch x65

Field 42'

Field 42'

P.

Brennan

99

98 WS 2 62

Cat NGC 2 5 39

RA Dec m AD Type Con 08 09 . 6 - 1 2 45 7 .9 20.5 II 1 m Pu.p 1 9 Pup (4 . 5 mag) lies c l o s e to the E . - - - - - - - - ( 1 2 ) 60 s t ars in 1 2' area . (8) Large , very numerous but faint ; dark bac k gr o � (6 ) Outline irregular and more or l e s s tri an�'l d. c� ar; contains many little clumps and pairs of star s . , 18 qui t e rich overall and very rich in places ; about 7 5 s tars , mos tly of 1 1 and 1 2 magI about 20' diam, -

2 63

NGC 2 548 M48

-

08 1 2 . 4 -05 43 5.2 30.0 Contains 5 0 s tars to 1 3 mag.

-

-

---

I 2 m

Hya -

-

-

..

( 1 2 ) 7 0 s t ars in 2 5' area; central group shape d like an el ongated l e t ter S . ( 8 ) Forms a di stinc t , almo s t equi l at eral triangle; many of the fainter s tars are grouped in small pairs; the surrounding sky i s qui te dark , and the cluster is

I.

NGC 2 5 39· 8-inch x40

NGC 2 548 - M48

Fi eld 6 5'

Fi eld 65'

Glyn Jones

8-inch x40

K.

Glyn J ones

qui te self-containe d; naked-eye obj e c t in a good s�.

2 64

NGC 2632 M44

Cnc 90.0 08 38 . 6 +2 0 0 5 II 2 m Contains over 2 000 star s . Doubles are numerous . The vari abl e S Cnc ( 8 - 1 0 mag: 9 . 48d) appears within the clus ter stars but i s not a member . -

265

NGC 2682 M67

-

.

In anything but a rich-fi eld telescope thi s clu s ter i s generall y too large for the fi eld of vi ew ; the er brighter s t ars have a yellowi sh hue , and one observ records a 9 mag greeni sh star near the cent re ; �. t is an easy naked-eye obj e c t . ---

Cnc + 1 1 54 7.5 II 2 m 14.5 Contains about 500 star s from 1 0 to 16 mag. .. .. - - - - - - - - - - - - - - - - - ( 8 ) Bri ght o b j e c t in a fairly dark part of the sk.y '' ill brighte s t s t ar i s on the NE edge and about 8 mag, to the central area there are about 20 s t ars of 1 0 1 2 magI more than 60 s t ars wi thin a 7' . 5 radiUS .

08 49 . 2

-

NGC 2632 - M44 8-inch x40 Fi eld 65'

NGC 2682 - M67 8-inch x1 00 Fi eld 40'

•

K . Glyn J ones

1 01

1 00 WS 2 66

Cat NGC 6405 M6

RA Dec m AD Type C on 1 7 38 . 4 -32 1 2 5.3 26.0 III 2 p Sea The s econd brightest s tar i s RD 1 60202 , a fl ar e s t� which showed a 5 mag increas e in 40 min in 1 9 65 . - - - - - - - - - - - - - - " ( S ) Rich , bri lliant clus ter containing group s Of small , faint stars among very many bri ght on e s ' , not e asily s e en from lati tudes hi gher than 50 0 N . ( 7 x 3 5 ) Large , beautiful clus ter , well s een . -

2 67

NGC 6475 M7

2 68

-

-

-

-

,

---.. 1 7 52 . 3 -34 48 50.0 Il 2 r Sea - - - - - - - - - - - - - - . A large cluster b e s t obs erved through the find e r t e l e scope ; a bright , fairly clo se pair i s at the centre with a yellow s tar SW of centre ; a 3-inch wi ll al s o give good re sul t s on thi s obj ect . -

-

-

27. 0

-

-

-

-

-

,

Field 2 5 '

Sgr

III 1 m

NGC 6494

1 7 55 . 5

M2 3

Contains about 1 20 s tars of 1 0 mag and below. - - - - - - - ( 1 2 ) 1 00 s t ars in a 2 2 ' fi e l d . ( 8 ) Fine , bright clu ster of 1 0 to 1 3 mag s tars; a 6 mag s tar i s clo s e to the NW , and the group shollS a fan-like shape spreading from an S mag s tar to tha NE ; main par t s fi t into a 40' fi e l d . ( 1 0 x 50 ) Large and bri gh t ; easily resolvable . -' sgr I 2 m 6.3 1 S 01 . 7 -2 4 2 3 Clus ter as s oci ated with NGe 6 52 3 , an emi s s ion nebula des cribed in Volume 2 . . - - - - - - - - - - - - In binoculars or small t e l e scop e s the clus t er caJl er be s e en to appear s l i ghtly nebulous ; the clust f·10 ient1Y i s not very rich or impre s sive , but i s suf t bright to be s een with the naked eye from Gr e a

- 1 9 01

NGe 6405 -' M6 1 2-inch x

I.

Glyn J ones

NGe 6475 - M7 8 x 50 Binoculars Fi eld 2 0

K . Glyn J ones

-

269

NGC 6 5 3 0 M8

-

-

Bri tain and the northern

U.S.A.

-

-

-

-

N Ge 6494 - M2 3 S-inch x1 00

NGC 652 3-30 - MS 8�-inch x51

Fi eld 40 '

Fi eld 4 5 '

E . S . Barker

103

1 02 ws

2 70

RA Dee AD Typ e 1 8 03 . 1 -22 30 12.0 I 3 m Con tains about 60 sta rs of 8 mag and bel ow ,. 1 al:'g clouds of obs curing dus t sur e rou nd the clu st er. - - - - - - - - - - .- ( 8 ) A sma lli sh . fairly compac t clu ste r at th e NE o f a dou bl e str ing of fairly bri ght stars wh i ch conn ect it with the nebula M20 ; rather sp ar s e and formle s s , about 20 sta rs bei ng vis ibl e . ( 3 ) Bright and easi ly re s olvabl e .

Cat NGC 6 5 3 1 M2 1

-

271

NGC 6568

-

Tr 3 2

NGC 6603 [M2 4]

-

-

-

--­ -2 1 36 13.0 III 1 m Sgr - - - - - - - - ... .... ( 8 ) Rather faint and ope n with few bri ght stars; an S-sh ape d curve in the c entre surrounded by a fine dusting of faint mem ber s ; 1 4 S gr ( 5 . 5 mag) lie s 20' to the E . ( 6 ) Sparse , with s ligh tly nebu lous centre ; 2 3 s tars, 1 8 1 6 . 1 -1 3 2 1 12.2 4.0 I 2 m Ser - - - - - - - - - ( 1 0) Very faint , smal l and diff icul t ; the brightest star is of 1 2 mag , and x 1 20 need ed to reso lve the few memb ers shown ; evid enc e of a very rich object requiring a l arge apertur e ; about 3 ' diameter . -

2 73

-

18 1 1 .3

-

272

-

-

-

-

-

-

-

-

K. Glyn

-

-

NGC 6 568

8-inch x40 Fiel d 6 5 '

8-inch x 1 00

Jones

Fie ld 40'

K . Glyn J ones

-

1 8 1 7 . 0 -1 8 2 5 1 1 .8 5 .0 I 1 r Sgr This clus ter is situated in a star -cloud , the latter bein g the obj ect catal o gued by Mes s ier . The c loud is about 1 . 5 0 in diam eter and of 4 . 6 mag . - - - - - - ( 8 ) NGC 6603 lies to the NE of M24 dire ctly N of a red or orange star ; s eems nebu l ous due to it s faintn es s ; at HP , in good conditio ns , it showS as a � den se c lUst er containing s ever al narrow , curve d dar l ane s ; M24 is an easy nake d-ey e obj ect , and a good vie w can be obtain ed by bin ocu l ars . -

NGC 6 5 3 1 - M2 1

-

-

-

-

-

-

•

TRUMPLER 3 2

NGC 6603 - M24

1 0-inch x1 20

8 x 50 Binoculars Fi eld 2 0

3' t

K.

Glyn J ones

t05

1 04 WS 2 74

Cat NGC 6 6 1 1 M1 6

RA m Dee AD Type 1 8 1 7 . 4 - 1 3 47 6.4 8.0 II 3 m Contains a large number of faint , red star s , po ssibly reddened due to obscurati on . ( 8 ) Si tuated at the N end o f a large , curv in g ' ' S of bri ght s tars ; a fine , conspi cuous clust er wi th nebulosi ty associat e d , details of ,.hi ch a:.:-e to b e found in Volume 2 .

275

NGC 66 1 3 M18

276

NGC 6633

---

8.5 1 8 1 8 . 5 - 1 7 08 7 .0 Il 3 p Sgr Thi s clu s t er i s obscured by 1 . 4 magni tude s . - - - - - - - - - - - - - - - - - - .. ( 8 ) Rather an inconspi cuous cluste r wi th one or tllo brighti sh s tars and the remaining fainter one s forming something of an ' S ' shap e ; rather diffi cult to pick out from many o ther groups in the region. ( 1 5 x 80 ) Appears rich and more compres sed . 1 8 26.3

+06 33

6.0

25.0

III 2 m

Oph

NGC 6 6 1 1 -' M1 6 8-inch x1 00 Fi eld 40 ' I. Glyn

Jones

NGC 66 1 3 - M1 8 8-inch x1 00 Fi eld 40 '

K . Glyn J ones

( 1 2 ) 35 s t ars in a 2 0 ' fi eld. ( 8� ) Large , loose clus ter wi th the majority of stars of 8 to 1 0 mag; a smal l , arrow-shaped group lieEl on the NW edge ; a fine LP field. ( 6 ) The bri ghter stars W-shaped ; a magnific ent group

easily vi sible ,to the naked eye . 277

lC 472 5 M2 5

-

sgr 6.5 35 . 0 I 2 p 1 8 30 . 3 - 1 9 1 6 Contains the Cepheid U S gr , discovered in 1 9 5 6 • -

- -

( 1 2 ) 40 s t ars in2 0 ' fi eld ; compac t c entre . ( 8 ) A fine , though rather open group wi th a dark . ne at backgroun d ; a bright , s l i ghtly yellow star l�eS e the c entre ; c an be a l i t tle diffi cult to se pa rat

from o ther nearby fields . ( 6 ) About 2 2 ' x 1 5 ' diamet er ; s tars of 7 m ag belo� , including one red ; fine group .

and

NGC 6 633 8 !-inch x 5 1 Fi eld 4 5 '

lC 4 72 5 - M2 5 8-inch x40 Fi eld 6 5 '

K . Glyn Jones

107

1 06 ws

2 78

Cat NGC 6645

RA 1 8 31 . 1

Dec -1 6 55

m 8.3

AD 1 1 .0

Type Con III 1 m s� - ( 8) A cloud of very faint s tars including a f ai�l bri ght triple ; about 60 s tars in a roundi sh sh Y ape over three quarters o f thes e being about 1 2 ma , g; 1 1 and 1 1 � mag outliers extend in all dir ect i on s, compri sing about 30 to 40 addi ti onal s tar s ; main body 6' , outli ers extend thi s to 1 0 ' . -

279

NGC 6649

6.0 10.1 1 8 32 . 1 - 1 0 2 5 Contains the Cepheid V 367 Sct .

II 2

-

-

-

-

NGC 6664

9.0 1 8 3 5 . 4 -08 1 5 Contains the C epheid EV S c t .

.

..

,

:. . : .. . . . . .... ." .. .. . . � ;. . : ,,

"

'

,

-

:;

:

Set

m

( 8 ) Located just NE of a 9 mag s tar ; coars e group about 4 ' in di ameter and roundi sh; contain s 1 5 to 2 0 s tars of 1 1 mag and fainter ; poor , but qui te defini t e ; b e s t at LP . ( 6) Faint , nearly 1 0' acro ss and barely resolved . 280

.:

:... '

-

Set

III 2 m

NGC 6645 8-inch x1 2 5 Fi eld 2 0 '

-

P.

Brennan

NGC 6649 8-inch x 1 2 5 Fi eld 2 0'

P . Brennan

( 1 2) 2 5 s tars i n 1 5 ' fi eld . ( 8 ) Coar se group of mo s tly faint s tars ; di splays a U-shape , opening to the sw, the maj ority of s tars being at the bas e o f the U ; ri ch main body , about 1 2 ' x 6 ' , containing about 30 s tars of 1 0 mag an d fainter ; alpha Sct ( 4 mag) l i e s to the W. ( 3) Faint , l arge and s cattered ; s eems very ri ch .

-------

281

NGC 6694 M2 6

Sct I 1 m The bri ght e st s tar in thi s clus ter i s 1 1 . 9 mag. - - - - - - - - - - ( 1 2 ) 2 0 s tars in 1 0 ' area , the bri ghte s t forming . a shape like the northern sky sec tion of sc orpio ( 8) Not very impre ssive but contains som e fa irlY dense patche s of faint s tars ; the c entr al four of brightest s tars form a ki t e shape and two armS

1 8 44 . 0

-09 2 5

9.3

9.0

-

-

-

-

-

faint s tars l i e to the N and S . y· ( 6) Rather poor ; 4 s tars plus s l i gh t nebul oS�. t

NGC 6664 8-inch x6 5

NGC 6694 - M26

Fi eld 40'

Fi eld 40'

8-inch x6 5

K . Glyn J ones

1 09

1 08 WS 282

RA 1 8 4 9 .5

Cat NGC 6704

Dec -0 5 1 4

m 9.8

AD 5.0

Type I 3 m

-

Con Set -

( 6 ) A smal l , faint , nebulous c luster about 2 ' in di ameter ; some 1 1 and 1 2 mag stars are scat t er e d acro s s and around i t , giving dimensions of about 4 ' x 2' ; observed at x6 5 .

283

-­ 1 8 49 . 7 -06 1 8 12.5 I 2 r Set Nuc . of S c t 0131 . Contains about 600 stars bright er than 1 4 . 8 mag. - - - - - - - - - - - - - - sight , one of the mo s t impres si ve ( 1 2 ) A beautiful wi th thi s aperture ; almo s t a glo bular . ( 8 ) An impr e s s ive , compact c lus ter; the dense st part in the shape of a fan or arrow-head with an 8 mag s t ar j ust inside the apex; the densest part i s about 1 0 ' or 1 2 ' di am eter. ( 6 ) Shows a s tarl e s s vacui ty and much nebulosity o f unresolved s tars .

NGC 67 0 5 M1 1

284

NGC 6709

N GC 67 1 6

NGC 6705 - M1 1 8-inc h x1 00 Fi eld 40 '

6-inch x6 5 Fi eld 4 5' p.

:Brennan

K . Glyn J ones

Aql III 2 m 1 3.0 7.6 1 8 50 . 3 +1 0 1 9 - - - - - - - - - - - - - - - ( 1 2 ) 2 5 s tars in 1 5 ' fie l d . ( 8 ) Fai rly c ompac t , wi th dark area in the cen tre ; fan shape t o the NE ; not very impr e s sive. ·n ·n (6) 1 5 = --:-_ _ ����� _ Sgr IV 1 P 6.7 1 8 53. 1 - 1 9 5 5 Thi s c lust er i s obscured by 0 . 4 magnitudes -. - - - - - - - - - - - - - - - - - - - - ( 8 ) 1 5 s tars in 1 5 ' fi eld ; o thers suspe c te d . ( 3 ) Bright , easily reso lvable .

________________

285

NGC 6704

__

NGC 67 09 8 i-inch x56

NGC 67 1 6 8i-in ch x56

Fi eld 45 '

Fi eld 4 5 '

C. Nugent

111

110

ws

286

Cat NGC 6 7 38

RA

Dec +1 1 34

1 9 00 . 2

m 8.5

AD 12.5

Type IV 2 p -

Con Aql �

..

' ( 8 ) Diameter from 8' t o 1 2 ' , there being a l ar ge number of outliers whi ch may be c lus ter or fi e l d s tars ; the richest c lump i s roundi sh and con t ain s 2 5 mag 9 s t ars , among them a wide 9 mag pai r ; many s tars arranged in pai rs and strings . ( 3 ) Faint , l arge and l o o s e ly grouped . 2 87

NGC 6 7 5 6

1 9 07 . 4 +04 3 7 10.6 P o s sible double wi th NGC 67 5 5 . -

-

-

-

-

-

-

-

-

-

-

289

N Ge 6 7 9 3

NGe 6800

19 22.1

"

..

I' ,

Aql

-

-

-2 2 08

•

--­

I 2 m

-

Sgr

IV 2 p

NGC 6 7 3 8 8-inch x7 5 Fi eld 42 '

- ..

( 8 ) The dominant feature i s a smal l , qui te bri ght nebul ous patch only partially reso lvable and about 0 ' . 5 in extent ; i t i s s e t in a group of about 1 5 1 2 mag stars that extend t o the W and S . 288

. . . .

P.

Brennan

NGe 67 56 8-inch x1 2 5 Fi e l d 2 4 '

P . Brennan

( 1 0 ) A very tight group clus tered in the centre of a fairly sparse fi eld ; a small tri angl e of 1 0 mag stars dominate s , and s everal wi de pairs are to be s een ; fairly rich and about 1 3 ' di ameter with 23 s tars seen; HP i s preferable . 1 9 26 . 1

+2 5 0 5

-

-

III 2 p -

-

-

-

Vul

-

-

- - -

( 1 2 ) 5 5 s tars in 2 0 ' fi e l d . ( 8 ) Contains about 30 mag 1 0 stars i n a 1 0 ' gr oUP; outliers extend thi s to nearly 2 0 ' and rai s e t he number of s tars to 45 or more , inc luding s e v e ral ui te 9 and 1 0 mags ; overall the c luster membe r s ar e q bright , the c luster giving the impressi on t hat addi tional members would be added by an i nor e ase l aperture .

fe�Il

NGe 6 7 9 3 1 0-inch x 1 20

NGe 6800 1 0-inch x8 0 1 0'

( 1 5 x 80 ) Faint , l arge and rich .

G. Hurst

113

112

WS 290

Cat Stock 1

RA

1 9 34 . 7

Dec +2 5 09

m 7.0

AJ)

Type 2 p

IV

60.0

( 1 0 ) S tars scattered acro s s the entire fi eld at �4 but i t hard�y resembl e s a clus ter ; 47 s tars in an 0, area of 40 1 , most prominen t are two rich group s eact containing a number o f neat double s . -

,

291

NGC 6 8 1 1

19

37.4

+46 3 0

III

11.5

1 p

-

-

Cyg -

( 1 2 ) 40 s tars in 1 2 1 are a . ( 1 0) A faint c luster rich in two main areas ; con s everal doubl e s including one of 1 0 mag in the E diameter 1 01 ; 3 5 stars . ( 1 5 x 80 ) Faint , very l arge and rich . 2 92

NGC 6 8 1 5

19 39.9

IV

+ 2 6 47

2 p

L

Cyg

( 1 2) 40 s t ar s in 1 5 1 x 1 0 1 area. ( 1 0) Large but not ri ch cluster in a superb fi eld; s tars of 1 0 mag and below are scattered throughout the fi eld , whi ch has a notic eable s t arles s area to the SW ; clus t er s tars all appear whi te ; 3 7 stars . ( 1 5 x 80 ) Faint , oval obj ect . -

-

STOCK 1

NGC 68 1 1

1 0-inch x40

1 0-inch x80 1 0t

40t

.

G.

G. Hurs t

Hurst

-

293

NGC 681 9

9.9

Cyg 5.2 I 1 r r S everal red giant s are members o f thi s cluste , the brighte s t being variable . ( 1 2 ) 60 s tars in 2 5' fi e l d . ( 1 0 ) Gli t tering group of small s tars n o t full y resolved at x1 2 0 ; resolved s tars are of 1 1 to 13 JDag s e t against unresolved nebul o si ty ; roughl y U_shaped, small and compact ; 2 1 s t ars ; diame t er 5 1 't y ( 6) Small group of 1 1 and 1 2 mag s t ars ; ne bul oS1 vi sible even in moonli ght ; 3t to 4t diam et er . 1 9 40 . 5

+40 08

-

-

-

-

-

-

-

-

-

.

NGC 681 9 1 0 - inch x1 2 0

NGC 68 1 5 1 0- inch x80

5t

( 1 5 x 80) Faint , very rich , tightly groupe d . G. Hurs t

1 15 1 14 ws

2 94

Cat NGC 682 3

RA

1 9 42 . 1

Dec +2 3 1 5

m 9.8

AD 5.5

Type I 3 p

( 1 2 ) 2 0 stars in 5 ' area; in ri ch 3 0 ' field . ( 8 ) Stands out only wi th averted vi sion ; at th e centre are 3 stars in a row, 1 mag 1 0 and 2 mag

1 1. , magi

.

about 30 1 0 mag stars in all , plus o thers o f 1 2 about 5 ' x 3 ' in size . ( 6 ) At times shows a nebulous appearance ; con tains qui te a number of faint s tars . 295

NGC 6830

1 9 50 . 0

+2 3 0 1

- - - - - - - -

8 .7

6.0

II 2 p

- '- - - - - - - - - -

--

Vul

- - -

( 1 2 ) 2 0 s tars in 7 ' area. ( 8 ) Main part i s irregularly round and about 4' to 5 ' in extent ; contains 5 s tars of mag 1 0 and 1 1 �d a score of mag12; x7 5 fairly rich and compre ssed , 296

NGC 6834

+2 9 2 1 5.5 II 2 m 9.7 Contains a number of infrared s tars . 1 9 51 .2

- - - -

- - - - - - - - - - - - -

Vul -

;

6-inch x1 2 5

NGC 6830 8-inch x1 00

Fi eld 2 4 '

Field 40 '

NGC 6 8 2 3

P.

. .

K. Glyn J ones

Brennan

- - -

( 1 2 ) 2 5 s tars in 1 0 ' area. ( 1 0 ) Very rich and compre ssed wi th inner groupings; needs a minimum of x1 2 0 to reso lve , appearing as a nebulous s treak at LP ; 43 s tars ; s i z e 4 ' x 3 ' . 297

NGC 6866

2 0 02 . 9

+43 5 5

9.0

7.0

II 2 m

Cy g - - -

( 1 0 ) Rich , c ompact group ; 2 bright l ines of s tars extend S , and an 1 1 mag close doubl e i s near the centre ; haze o f unresolved stars ; 2 1 s tars se en . (st) Cons i s t s mainly o f faint stars in fai rl y tight formation ; s everal double s involved , and se ve r al brighter stars in the fi e l d . ( 6 ) Fairly bri ght and small s tars wi th nebul o s i ty .

NGC 6866

NGC 6834

1 0-inch x 1 2 0

6-inch x1 2 5 Fi eld 2 4 '

1 0'

G. Hurs t

117 1 16

WS 298

Cat NGC 6 8 7 1

Dec RA m AD Type C on 6.0 2 0 04 . 9 +3 5 42 30 . 0 IV 3 p CYe Contains a number of infrared s tars . - - - - - - ( 1 0 ) Cons i s t s of 2 bri ght doubl es wi th all th e oth e� s t ars much fainter plus some haze o f unre sol v ed st a�a, contains the doubl el: 2 6 3 0 , a yellow pair of 7 ma 15, 1 6 s tars ; 1 0 ' di ame ter . ( 8 ) x1 7 0 5 5 stars in 2 0 ' area; s everal mul ti p le st -=ars, 1 3.1 2 0 09 . 5 +41 08 63.0 II 3 r Cyg - - - - ( 1 0 ) Very smal l , faint , compact group wi th a glo w in the background sugge s ting a rich obj ect ; very diff 1 3 s tars at x1 2 0 ; 6 ' di ame t e r . -

-

-

-

-

-

-

'

>

-----------------_______________

299

IC 1 3 1 1

-

-

-

-

-

-

-

-

( 8t ) x1 1 6 and x2 32 a s tar of 1 2 mag accompani e d by of 1 3 mag a li ttle to the NW and enveloped in ne 300

NGC 6883

20 1 0. 3

+35 46

1 1 .5

I 3 p

NGC 6885

Cyg

Vul III 2 P 7.0 9.1 Superimpo sed upon NGC 6882 . ( 1 0 ) Bri gh t , wi th yellow 2 0 Vul ( 6 mag) at th e cen tte'> con tain s rich and barren areas . ( 8 ) x1 7 0 the two clus ters 6' apart , the sep ar a t'�on being somewhat arbi trary ; 1 5 s tars s e en in 68 8 2 and

20 1 0. 9 -

-

+2 6 2 4

-

-

-

-

-

-

-

-

-

-

-

Fi eld 3 0 '

6'

one

( 1 2 ) 40 s tars in 1 5 ' are a ; rich fi eld . ( 1 0 ) Compac t group consi s ting of a bright 1 0 mag double wi th an arrow of s tars t o the E ; fairly ri ch in a quite d en s e fi eld; 2 1 stars ; 1 2 ' di ame ter . ( 8-k ) About 1 5' di ameter cons i s ting o f white star s of about 9 to 1 1 mag; no nebul o s i ty in the area, but there are several bri ght double stars to be s een . 3 01

IC 1 3 1 1 1 0-inch x1 2 0

NGC 687 1 8t-in ch x7 7

8.J.

G. Hurs t

Hynes

'0

•

-

NGC 688 5 1 0-inch x80

NGC 6883 8t-inch x7 7 Fi eld 3 0 '

12'

3 0 stars in 688 5 .

G . Hurs t

119 118

WS 3 02

Cat Rup 1 72

RA

20 1 0 . 9

Dec +3 5 33

m

AD 4.0

Type I 3 p

( 1 0 ) Tri angl e of 1 1 mag s tars wi th rays of s t a� s extending from points o f the tri angl e ; a 1 2 mag double l i e s in the W par t ; no s tars are wi th in the triangl e t o a limi ting magni tude of 1 4 mag; in t he same LP fi e l d as NGC 688 3 ; 2 1 s tars ; 5 ' diamet er --------------------------------------- -------------I C 4996 2 0 1 5 . 5 +37 3 3 7.2 303 5.6 I 3 p eyg

•

• . .

.

•

�

-

-

�

( 1 0 ) Semi-circle of stars showing nebulous at Lp.t x 1 2 0 elongated haze i n a fine fi e l d ; a 9 mag star i s on the N edge ; 2 0 s tars . ( 8! ) A beautiful clus t er in a ri ch fi eld; i t consists o f 3 mag 9 s t ars , the central one being slightly orange in colour ; trai l ing to the SE o f the se is a

mi s ty s tring of faint s tars , the bri ghtest being about mag 1 2 ; the who l e clus ter s eems to be in a faint envelope of nebul o s i ty .

of

304

er 41 9

20 1 7 . 2

+40 3 8

Cyg - - - - -( 1 0 ) Compact , but not ri ch ; s i tuat ed just to the N o f the double E. 2666 ; contains s tars o f 1 0 to 1 3 mag, including an 1 1 and 1 2 mag double ; 1 4 s tars . -

305

Dol 5

20 1 9 . 6

+39 1 8

lC 499 6 8!-inc h x1 54 Fiel d 1 5 '

RUPRECHT 1 72 . 1 0-i nch x1 2 0 L G.

5'

S. J. Hyn e s

Rur st

IV 2 g

7.0

IV 2

P

Cyg

- - - - ( 1 0 ) Very faint cluster enclo sed by a trap ezi um of 1 0 mag stars ; members are evenly di s tri bu ted and o f 1 1 mag and below.

.

DOLI DZE 5 1 0-in ch x1 2 0

COLLlNDER 4 1 9 1 0-in ch x1 20

7'

4'

t

G. Hurs t

121 120

WS 306

Cat Cr 42 1

3 07

NGC 69 1 0

3 08

NGC 6 9 1 3 M2 9

RA Dec m AD Type Con 2 0 2 2 . 4 +4 1 37 6.0 9.9 III 1 p eYe - - - - - - - - - - - - - - - - ... (1 0) 1 0 mag triangular group wi th fainter s tars to , the W; moderately ri ch ; no doubl e s ; 1 8 s tars .

2 0 22 . 2 +40 42 Related to Cyg OB1 .

1 1 .0

I 2

P

•

- - -

( 1 0) Bri gh t , loose group containing 2 promi n en t t s ars joined by a line of fainter one s ; 1 4 s tars . ( 8) Coarse cluster wi th a peculiar branched shape ; dominated by 2 mag 9 s t ars , both deep yell o w-or ange in colour ; about 2 0 mag 9 s tars are include d and the remainder are of mag 1 1 wi th a few fainter ones; the main body i s elongated W-E ; s tands out well in field, III 3 p 9.1 2 0 2 3 . 0 +38 2 7 Cyg Thi s cluster contains a number of infrared s tars

i s obscured by 3 magni tudes . 6 s tars bri ghter 9 . 5 mag. Di ffuse nebul o s i ty lies around.

�d

COLLINDER 42 1 1 0- inch x 1 2 0

NGC 6 9 1 0 1 0 - inch x8 0 8'

G.

Hurst

G. Hurs t

thM

( 1 2 ) Di sappointing; only a few s tars in a loose group, ( 8) Very spars e , cons i s ting of 7 or 8 fairly bri ght s t ars , the 4 bri ghte s t forming a quadrilate ral and ano ther 3 a small tri angl e to the N ; only a few other faint st ars are in the vi cini ty . ( 6 ) 5 ' di ameter; contains a red s tar . --------� Cep 20 3 0 . 9 + 6 0 3 3 I 1 m 7.0 10.2 309 NGC 6 9 3 9 - - rs ( 1 6� ) Large , ri ch group wi th the brighte s t membe in the SW end , whi ch i s the dens e s t part . JIlost ( 1 0 ) I rregular shape wi th the W and S ends the in di s tinc t ; few st ars resolved , the remainder sho w g

NGC 6 9 1 3 - M2 9 8- inch x1 00

NGC 6 9 3 9 8 - inch x 1 00

Fi eld 40 '

Fi eld 40 '

as a greyi sh glow ; in a poor fi eld . ( 8) 5 mag 1 1 st ars and many fainter ; diffus e overall shape like a ki t e .

J ones

K.

Glyn J ones

123 122

WS 310

Cat NGC 6940

RA

Dec +28 1 3

20 3 3 . 5

m 7.1

AD 32.5

Type III 2 m

- .. ..

( 1 0) Ri ch , bri ght group wi th a compre s s ed ar e a S Of a 1 0 mag red st ar at the c entre ; contains many doubles and triples . ( 81.2 ) M aJ or aXl" s In PA 1 60 0 - 340 0 ,. d ens e 1 y POPUl ated in the S part ; 9 1 s tars. ( 8 ) 50 s tars in 45 ' fi eld ; faint . '

311

Rup 1 7 3

2 0 40 . 8

+3 5 2 7

50 . 0

III 2 p

--­ Cyg

- - - ...

( 1 0 ) A very large , loo s e , coarse group ; the brighter s tars cover an area ab out 2 0 ' acro s s , but few stars are bri ghter than 1 3 mag; 50 s tars in a LP field �d 3 4 s tars in the clus ter region. 31 2

313

Rup 1 74

Rup 1 7 5

5.0 Il 2 p Cyg - - - - - - - - - - - - - ( 1 0 ) The X on the chart oppo site shows the position of thi s clus ter , whi ch i s therefore beyond the reach of thi s aperture ; the field i t s elf i s of interest, containing a doubl e s tar marked A in the chart , both s tars are ab out equal and whi te in colour ; the fhld di splays st ar-poor regi on s . 20 42 . 5

NGC 6 940

RUPREGHT 1 7 3

1 0-inch x80

1 0-inch x80 5'

+36 5 7

G. Hurst

••

A

Cy g - - - - ( 1 0 ) Irre gular s emi-circ l e of s tars enclosi ng a st arl e s s area; not a ri ch group ; a 1 3 mag doubl e I,le s on the SW edge ; 2 7 s tars at x1 2 0 . 20 44 . 2

+35 2 5

9.0

III 2 p

RUPRECHT 1 74 1 0-inch x80

RUPRECHT 1 7 5 1 0-inch x 1 2 0 1 3'

G . Hurst

125

124

ws

314

Cat NGC 7063

RA 21 23.4

Dec +36 2 3

m 8.9

AD 12 . 0

Type III 2 p

Co n

CYg - -

( 1 0 ) A generally bri ght cluster containing s t ar s of 1 0 to 1 2 mag whi ch are fairly loose and even ly di stributed ; a pair of s tars at ' A ' on the ch art oppo site resolved at x1 2 0 , 1 2 and 1 2 . 5 mag and V r e y clo s e ; 1 S stars ; 7 ' di amet er . ( S ) 3 5 s tars i n 2 0 ' are a ; very bri ght . 315

NGC 70S2

2 1 2S . 5

25.0

+46 5 9

IV 2 p

-­ Cy g - - - ...

(st) Moderate si z e , about S ' ; consi s t s of a mixture o f bri ght and faint whit e s tars of 1 0 to 1 3 mag i one or two double s . ( S) Pre tty scattered wi th about 8 bri ght stars in a s traggling group of fainter one s ; not very different from the background . 316

NGC 70S6

2 1 29 . 7

+51 29

1 1 .6

6 .0

II 2 m

NGC 7 06 3 1 0-inch x8 0

NGC 7 08 2 S�- inch x1 1 6 Fi eld 1 5 '

7' G.

S .J . Hynes

Hurst

Cy g

( 8 ) A smal l , fairly i s o lated clus ter containing few bri ght s tars but many faint one s ; about 1 0 ' diameter; not very impres sive . 317

NGC 7092 M39

-

Cyg 5.1 III 2 p 32 . 0 2 1 3 1 . 3 +4 S 20 Contains ab out 2 0 stars between 7 and 1 0 mag. - - . - - - - - - - - - - - - f ( S ) Very large group , but rather sparse ; 3 s tar s o mag 8 l i e at the corners of a large , almo s t equi­ lateral tri angl e wi th the S side aligned E-W ; m�Y s tars in pairs including a bri ght pair near the l i e s in a very ri ch region. ( 1 0 x 5 0 ) Very bri ght and large ; resolvable .

"

..... . •

, .

NGC 7 08 6 8-inch x 1 00 Fi eld 40 '

NGC 7 092 - M 3 9 S-inch x40 Fi eld 6 5 '

K . Glyn J ones

12'7 126

WS 318

Cat NGC 7 1 2 7

RA

2 1 43 . 0

Dec +54 30

m

AD 2.8

Type IV 2 p - - - - - -

Con

cY-g

( 1 2 ) 1 0 s tars in 2 ' area. ( 1 0 ) Compac t group showing considerable haz e o f the unre solved members ; s tars of 1 0 to 1 3 mag; 8 st ars , ( 6 ) 5 faint s tars and nebul osity; very small . 319

320

NGC 7 1 2 8

NGC 7 1 42

2 1 43.2

+53 36

1 1 .4

II 3 m

- - - ( 1 2 ) Unresolved except for 4 stars ; 3' diame t er . ( 1 0 ) Small , nebulous patch wi th 5 s tars embedde d; a 9 mag s tar on the SE edge. 2 1 45.3

+65 4 1

9.6

II 2 r

-

Cep -

-

NGC 7 1 60

21 53.0

+62 3 9

5.0

1 0-inch x80 2'

- .

( 6 ) A round c luster, qui te ri ch , but wi th all its members very faint ; more than 2 5 stars evenly di s tributed in an 8 ' area ; a 9 or 1 0 mag star lies on the N edge ; a difficult group. 321

NGC 7 1 28

NGC 7 1 2 7 1 0-inch x 1 2 0

G.

G . Hurs t

Burst

Cep - - - -( 1 2 ) 1 5 stars in 1 0 ' area; one double , one triple. II 3 p

( 1 0 ) Tri angle o f stars at the centre including 2 of mag 8 ; haze of unresolved stars. ( 8� ) 2 5 stars ; brightest trend E-W. ( 6 ) About 7 ' diameter ; 2 mag 8 stars , 5 of mag 9 1 0 and s everal of 1 1 to 1 2 mag .

stars

to

NGC 7 1 42 6-inch x6 5

NGC 7 1 60 1 0- inch x80

Fi eld 45 '

7'

G. Hurst

1 29 1 28 WS

322

Cat NGC 7209

RA 22 04 . 2

Dec +46 22

AD 16 . 5

Type III 1 p

Con

-

-

Lac

•

-

(12 ) xSO 50 stars in 20 ' are a . (S� ) Diffi cult to define the borders ; sparse s t ar dis tribution to the S ending in a starless lane. , a yel l o w star li es to the N and a few faint pai rs are to be seen ; maj ori ty o f stars are 9 to 10 mag. ( S ) Dis tinct cluster wi th few bri ght stars but Very

many 9 , 10 and 11 mag; rather straggling. ( 6) About 15 ' diame ter ; stars wi th nebul osi t y. -----IC 1434 22 09 . 7 + 52 42 9.6 6.0 II 1 p Cyg -

-

-

-

(10 ) A very faint , medium s i z e c lust er containing interesting groups of very faint stars in groups, particular a 13 mag group of a few c l ose stars on

-

Fi eld 4 5 '

in

the

N e dge ; consi derable haze evident , possi bly nebulous in parts ; si tuated in a glori ous regi on; diameter 71; 21 stars seen . 324

325

NGC 72 3 5

NGC 7243

22 11 . 7

+57 09

4.0

III 2

P -

-

Cep -

-

-

IC 1434 10-inch xSO

NGC 7209 S�-inc h x51

E.S.

Barker

G . Hurs t

-

( 6 0 ) 2 5 stars in 3 ' area plus some outli ers . magB (10 ) Small group c onsisting o f a tri angl e of and 2 mag 9 stars plus ano ther S fainter ones ; some haze o f unresolved members also evi dent . S ( 6 ) x96 a 9 mag yellow star at the E end ; oth er star 10 and 11 mag; 4 ' x 3 ' di ameter . ---

Lac 22 14 . 3 +49 4 5 6 .s 30.0 IV 2 p Contains eight possible spec trosc opic binary stars. ; (12 ) SO stars in 22 ' x 16 ' area ; like two clusters ntre• double star wi th e qual whi te components ne ar ce (S�) Triangular shape wi th points to the NE , NW �d -

S;

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

ar­

red star to the N o f the c entral double ; a st l ess l ane runs NW to SE; 6 9+ stars ; 30 ' diameter. b16' ( 1 5 x SO ) Large , bright and ri c h ; easi ly reso1va

NGC 7243

NGC 723 5

-

10-inch xSO 4' L t

10-inch xSO

G . Hurst

131

1 30 WS 326

Cat NGC 7245

Dec m AD Type Con 11.5 +54 1 2 II 1 p 5.0 Lac - - - - - - - - - - - - - - - - - - .. .. ( 1 2) S everal groupings ; ri che s t 1 5 s tars in 6 ' al:'ea ( 1 0) Very faint and containing some haz e ; only at' !\ s tars reso lved , the brightest to the S . ( 8t) Triangl e o f 8 , 9 and 1 0 mag s t ars wi th faint e� one s suspected ; 6 s tars only seen.

327

IC 1 442

22 1 5.4

328

NGC 7 2 6 1

RA 22 1 4 . 5

II 2 m Lac - - - - - - - -" ( 1 0 ) A c lustering o f faint s tars surrounding a 8 �� reddi sh s tar and one o f 9 mag; not rich and easy to overlook during a sweep ; x80 2 0 s t ars ; 9 ' diam eter. 22 1 9 . 5

NGC 72 8 1

•

+53 54

+57 58

9.8

-

6.0 III 1 p - - - - - - - -

-

-

Cep -

2 2 2 3 . 8 +57 43 IV 2 p Doubtful whe ther thi s i s an ac tual c luster. -

-

-

-

-

IC 1 442

NGC 7 2 4 5 1 0-i nch x80

-

1 0-inch x80 9'

- - ...

( 1 2 ) 1 5 s tars in 6 ' are a . ( 1 0 ) Compac t , appearing a s a double s tar o f 8 and 9 mag at LP; 8 s tars in all s e en at x80 wi th fainter members unr e so lved . 329

•

G.

G . Hurs t

Burs t

Cep -

-

-

- -

( 1 2) 2 0 s t ars in 1 0 ' are a ; faint . ( 1 0 ) A l arge , bri ght c lus t er but not very rich; chain of 3 mag 8 s tars prominent ; 1 8 s tars in all .

NGC 7 2 8 1 1 0-inch x80

NGC 7 2 6 1 6-inch x65 Field 42 '

G . Hur s t

13313 2 ws

3 30

Cat N GC 7296

RA 22 27 .2

Dec +52 1 0

m 1 0.0

AD 4. 5

Type 2 p

-

III -

-

-

Con

-

-

-

Lac -

( 1 2 ) 1 5 stars in 4 ' area . ( 1 0 ) Li es be twe en an 8 and 9 mag star ; ext en de d ' In a N-S line wi th 2 curves o f faint stars at th e C ent x80 1 6 stars ; 8 ' diame t er ; in a very rich region �ei ( 8! ) A smal l , rather inconspi cuous c lust e r , a li tle di ffi cult to l ocate in a rich fi e l d ; about 5 ' di�. and consists o f 1 1 t o 1 3 mag stars l e d by a 9 mag one-I a dis tinc t nebulous glow o f unreso lved stars

�

331

NGC 7 380

8.0 III 3 p Cep The stars in this c luster e m: i t p o l ar:Lsed light d ue to the presenc.e - - . ( 1 2 ) 20 stars in 20' area; very symmetri cal . ( 1 0 ) Faint , ri ch group wi th primary an 8 mag yellow s t ar ; 1 3 mag doubl e on S e dge ; stars s e t against a background glo w ; 26 stars . 22 46 . 0

+57 58

8.8

-

3 32

NGC 7 5 1 0

23 1 0 . 5

+60 26

9.6

2.5

-

II

-

-

-

NGC 7 38 0

NGC 7296

---....

1 0-inch x80

10-inch x80 L

7'

8'

-

G.

G . Rurst

Burst

Cep

2 m

( 1 2 ) 1 0 bri gh t stars and many fainte r ; 3' diameter. ( 1 0 ) Distinc t ly oblong patch o f haz e at LP ; very small and rich ; contains a red 1 0 mag star. ( 6 ) Shows as 2 stars and nebul osi ty at LP ; 2' diam.

--------�

333

Mark 5 0

Cas 23 1 4 . 2 + 6 0 2 0 I 2 p 1 .5 Consists of the visual binary RD 2 1 9460 ( WN+B'O, V = 1 0 . 03 , separation about 1 " ) . This is surro unded by a compac t group o f e arly-type stars . The age of the c lust er is about 1 07 yr . ... - - - - n o ( 1 0 ) Appears as a nebul ous star at LP ; at x1 2 0 lY a.t11 a few members visi ble above 1 3 mag , and i t is ale a hi ghly c, o mpressed object ; 1 3 stars , 3 ' di am eter. -

-

-

-

MARKARIAN

50 1 0-ine:h x120

NGC 7 5 1 0 1 0-inch x80

-

3'

t

G . Rurst

13 5

134

ws

3 34

Cat NGC 7 6 54 M 52

Dec RA AD Type 23 2 3 . 1 +61 2 7 1 3 .0 I 2 r Contains about 1 90 stars of 1 1 mag and fai n t e� - - - - - - ( 1 2 ) 20 s tars in 1 0 ' area; bright . (8) Small group containing a few conc entration S of faint s tars and an 8 mag orange star ; incons Pi c uous ( 1 5 x 80 ) A few s tars resolved ; extension to NE. ' -

335

NGC 7 788

-

-

-

NGC 7789

-

•

-

�

--­

7.0

I 2 p Cas ( 1 0 ) Ri ch , compr e s s ed group showing consid e rabl e haz e ; diffi cult to resolve ; 8 s tars ; 4 ' diamet er . (8!) About 2 ' acro s s and c entred on a 9 mag star; six s tars wi thin the group enveloped in a dense nebul o s i ty whi ch i s almos t res o lved . ( 1 5 x 80) Faint , opaque cloud . -

336

-

-

-

-

Il 1 r 2 3 5 5 . 8 +56 3 5 About 200 s tars , 34% in the central region.

-

-

NGC 7 654- M52 8-im:.h x. 1 OD Fi.eld 40 '

NGC 7188

-

Cas

I. Glyn

8!-incn x1 54 Fi eld 2 0 '

S . J . Hynes

Jones

( 1 0 ) Very l arge , faint s t ar cloud showing as a

luminous glow at LP; diffi cult to fully resolve; at x80 bri ghter members only reso lved agains t a rich b ackground of haz e ; very ri ch and compre ssed at the c entre ; 3 3 stars ; 20 ' diameter. 337

NGC 7 7 9 0

Cas 23 5 7 . 2 +6 1 04 III 2 p Contains Cepheids CE Cas a & b and CF Cas . . ( 1 0 ) Arrow-head shape pointing NNE ; the S end i s formed by a square o f s t ars and a 1 3 mag tri an gle o f stars l i e s on the E edge ; 1 5 stars s een . C8!) Small group c ontaining stars o f 1 0 to 1 3 magi enveloped in nebulo si ty which i s concentr ate d in seell parti cular towards the E side ; 1 1 s tars cl e arlY -

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

NGe 7 7 9 0

NGC 7789 1 0-inchx80 20'

8!-inch x1 54 Fi eld 2 0'

including a c l o s e double . S .J . Hynes

1 37

A Catalogue of Open Clus ters .

part Two

De s criptions of a Further 29 Open Clusters .

138

WS

338

Cat NGC 103

RA

Dec

00 23.9

+61 12

Nuc . of Cas

OB4 .

m

Type Con p Cas Contains emi s s ion-line star s .

C at NGC 956

II 2

10.8

- - - - -

(8) 30

NGC

133

00 29.7

IV 1

+63 13

Nuc . o f Cas

OB4.

Cas

p

- - .. ..

�

extended grouping; major axi s abol1t ,.� mag cl os e double near the cent re . (8) 15 s tars in 10'; probably fainter s tars too ; 13' S E l i e s NGC 146. (10) 9 s tars in 0 0 170 - 350 ; 10

340

NGC

146

(10

x

NGC

146.

80)

00 31.6

Combines into a l arge clust er comple x +63 08

IV 3

6.0

Contains emi s s i on-line s tars .

s tars in 8' diameter group ; contains a 10 m88 doubl e ; major axi s in a N-W line ; fine fields in the regi on of thi s clust er and NGC 133. (8) 15 s t ars in 10' area ; twin of 133 but fain ter .__ (10) 13

341

Mel

15

NGC

1444

with

Cas

p

Type

Dec

IV 1

+44 33

p

Con And

(6) Li e s between a pair of 9 or 10 mag s tars , and extends more to the northern of thes e ; most members are faint , and the main part i s formed by an arc o f 5 s tars running alongside the E side of the pair o f s tars mentioned above ; about 6' x 3' in s i z e , and appears s lightly nebulous at LP .

s tars in 40' field , mo s t lying centrall y . (10 x 80) S t ands out clearl y , al though s ituat ed ina fi eld o f many clus ters . 339

RA

02 31.1

139

Hyade s

03 47.5

+52 35

6.4

3.0

IV 1

p

Per

Contains the doubl e star Z 446. - - - - - - - - - - - - - - - - - - - (12) 15 s tars in 15' fie l d ; not impres si ve . (s) Surrounds a doub le star wi th a 9 mag primary ; the c lu ster is about 3' x 2' in extent and e l ongated NW­ SE ; contains no more than 10 s tars , all 12 mag and fainter ; a coars e , poor and small obje c t . 04 25.0 +15 53 o.s 320.0 I 3 m Tau The Taurus Moving Cluster. The di s tance to thi s group has recently been revi s e d , and i s now put at a fi gure of about 40 pc .

Being a l arge , l o o s e group , the Hyades was not the Cas p subjec t of any tele scopic observations; binoculars Thi s c luster i s immersed in emi ssion nebulos� ty, which b eing the i d�al instruments to use for i t s s tudy ; i s I C 1805, and i s about 120' x 120' in di ame ter . HII too well-known for any description ; dUe to i t s s i z e pho tographs show a loop of emi s sion surroundi ng the an d nearnes s , i t i s an easy naked-eye o bject . ----------------- --�--------------------------------c lus t e r , i dentified wi th the radio s ourc e W4. Nel 15 "-�5 liGC 1624 11.S 04 38.4 +50 24 I 2 p N Per i s obscured b y about 3.8 magni tudes . - - Connected wi th emi s si on nebulo s i ty . ntre e c he t (8i) Scattere d , wi th the riche s t part at g i9 (s) Cons i s t s of an 11 mag s tar and about 6 mag 12 where there is an oval ring of 19 s tars; the r�n ones ; surrounded by nebulosity, bo th thi s and the about 5' x 2'.5 in s i z e ; no nebul o s i ty s e en . llesl 0 er 0 c lu st er being elongated NW-SE; nebul o s i ty 3' diam . (6) A group of bri ght s tars and about fa�n t 02 30.6

+61 19

6.6

21.0

HI 3

o

o

35

rich towards the c entre ; about

20'

diameter .

1 40

ws

3 46

Cat NGC 1 746

RA

AD

Type Con 05 02 . 1 42 . 5 III 1 p Tau. - - - - - - - ( 1 2 ) 50 stars in an irregular group ; about 2 5 ' a C:toss wi th some outli ers . ( 1 0 ) More concentrat ed on the E side ,· rich c 1us te:t ' Dec +23 47

m 6.2

and a dense centre ; 54 stars including a quadruPl e 1 mag 1 0 and 3 mag 1 3 . ( 8 ) 30 bright stars in a group almo s t 1 0 acro ss .

3 41

348

NGC 2 1 1 2

NGC 2 1 26

C at N GC 2 2 50

06 01 . 0

+00 2 3

+49 54

8.6

8.8

;;;-N- GC 2 2 6 9

NGC 2 3 3 1

( 1 2 ) 1 5 s tars in 1 5 ' fi eld .

34 9

350

NGC 2 1 86

NGC 2 1 92

( 6 ) A poor sight , requiring averted vi sion to about 5 ' in extent and i rregular in form ; cont ains 1 5 mag 1 1 stars and a mag 6 star l i e s on the NE e dge . -

354

NGC 2 3 7 4

06 1 3 . 4

+05 28

+35 52

9.0

10.9

6.0

III 1 p

- - -

.

( 1 4 ) Faint group in a rich fi e l d ; all s tars r e s o l ved ( 8 ) 2 0 faint stars i n an amorphous group ; 1 0 ' di am · oss ( 6 ) Ab ou t 1 2 very fa�n . t s t ars even I y scatte r "� d ac r a slightly nebulous background ; in a ri ch fi e ld .

Con Mon

A

06 42 . 6

Il

+04 3 5

2 p

Mon

07 05 . 7

IV 1 p

+27 2 4

Gem

07 2 2 . 9

1 0.0

-1 3 1 2

II 3 p

CMa

( 1 2 ) 2 5 stars in 1 2 ' fi eld . ( 6 ) Irre gular clus ter wi th nebulous region to the S

Ori Il 2 p . 355 NGC 242 1 - - - - - - - ( 1 2 ) Weak group ; 2 5 s tars in 1 5 ' fi eld . ( 6 ) 1 1 and 1 2 mag stars plus fainter ; di ffi cul t .---,

06 1 0 . 7

8.0

Type IV 2 p

( 1 2 ) 2 0 stars in 1 5 ' fi eld . ( 8 ) Roughly triangular in shap e ; most members faint wi th some of 9 mag; s everal faint pairs ; 1 5 stars .

Aur 1 p - - - - - - - - - --

b e se en;

AD

nebul o s i ty breaks up into extremely faint stars and a coarse halo of simil ar s tars surrounds the main body ; located in a fairly ri ch fi eld .

11

( 8 ) 100 s e group of about 1 0 to 1 5 stars .

m 8.9

( 6 ) Very much elongate d , about 3 ' x 1 ' , and shows as nebulous ; an 1 1 mag star l i e s at the centre ; the

9.0

6.6

Dec -05 01

small , coars e cluster of faint s tars wi th 1 2 members of 1 1 mag and fainter ; a 9 mag star lies on the N edge ; elongated E-W and about 5 ' x 4 ' in size ; stands out qui te well wi th averted vi sion .

--...... Il 3 m Ori Contains about 90 s tars of 1 0 mag and below. - - ( 6 ) A very coars e , inconspi cuous clus ter; cont ain s about 7 to 1 0 s tars of mag 1 1 and fainter which are scattered in a regi on 3 ' x 1 ' . 5 elongated NW-SE; a 9 mag star lies close to the NW.

05 2 5 . 6

06 3 1 . 5 (6)

ln€! Of

RA

141

whi ch res olves into faint s tars at x1 2 0 . 07 35 .2

-2 0 3 3

8.6

8.0

I 2 m

Pup

( 1 0 ) Well-defined , fairly ri ch , compact cluster; 8 fairly bri ght s tars and more fainter one s ; 8 ' di am . "-----Pup 356 Me l 72 II 1 P 9.0 07 3 6 . 2 -1 0 22 ( 1 0 ) A very ri ch congregati on of faint s tars ; 7 '

i n diameter and irregularly round ; s tars concentrated towards the centre ; very like a globular clus ter.

1 45

1 42 WS 3-57

Cat NGC 2453

RA

m 9 4

AD 5.0

Type I 2 P - - - ( 1 �) 20 s tars in 4 ' area ; neat group . ( 6 ) A very small cluster of 1 1 mag and fai n ter triangular in shape and about 2 ' in exten t ; x65 On), 8 s tars resolved; a 9 mag s t ar l i e s c l o s e NW . 07 46 . 7

Dec -27 1 1

-

3 58

NGC 2 47 9

07 5 3 . 9

-1 7 3 9

9.8

9.0

�

�

III 1 m

( 1 2 ) 30 very faint s tars in 1 0 ' area.

3 59

]I

( 1 0 ) Made up of approximately 40 rather faint s t1ll's, half being only vi sible with averted vi sio n ; at X 51 appears nebulous ; diameter about 1 0 ' . 2

07 54 . 3

-2 5 44

9.0

6.0

II 2 p

-

( 1 �) 40 s tars in clumpy groups ; 5 ' acro s s . 360

NGC 6 507

1 7 58 . 2

-1 7 2 3

7.5

7.0

Pup

-

IV 2 p

19

18 16.1

-1 3 22

12.1

I 2 m

of

N,GC 6 7 5 5

1 9 06 . 5

+04 1 0

1 0.0

IV 2 m

-

-

-

-

Sgr

Aql

-

-

-

- -

( 8 ) 2 groups of 1 0 to 1 5 s tars , each 4 ' acro S S . ( 6 ) 9 to 1 1 mag s tars plus faint nebulosity . � 20

1 9 52 . 0

+1 8 1 6

9.5

7.0

II 2 p

-

-

Sge -

( 1 2 ) 40 faint s tars in 1 2 ' area ; two cen tres� 364

NGC 7062

2 1 22 . 3

- - - -

+46 1 6

1 1 .7

4.5

III 1 p

eyg

.. ..

- - - - - - - - - - - - - - - �bieb

( 1 0 ) Nebulous at LP ; a faint , compact clus t er

i s extended NW-SE .

Con Type AD RA Dee Cep I 1 P 2.5 22 09 . 6 + 5 5 1 7 Related to Cep-Lac OB1 . - - - - - - - - - - - ( 6 ) x6 5 a faint nebula , formle s s and about l ' in extent ; i t l i e s SE of the southernmo s t member of an 1 1 mag pair ; the nebulo si ty shows slight c entral brightening, and 2 fairly ri ch kno t s of faint s tars lie clo s e to the E ; in a very ri ch fi e l d . 2 3 48 . 6

+67 53

10.0

1 1 .5

II 2 p

Cep

( 1 6�) Rich group , consis ting of small s tars set in a rectangular shape ; maj or axi s NW-SE , and 2 bri ght s tars lie near the N edge . ( 6 ) A coarse cloud of 2 0 to 2 5 s tars s cat tered over a 1 0 ' x 5 ' area; a few s tars of 1 1 mag are vi sible , but mos t are of 1 2 mag; near the W end i s a very elongated and qui te ri ch group of 1 1 mag s t ars whi ch

9 or 1 0 mag on the S edge ; contains about 12 stars in an area 8 ' x 4 ' extending NE-SW ; not conspicuous. .

( 8 ) 8 ' di ameter ; a spangle o f faint s tars .

1:f

- - .

S gr

( 6 ) A coar s e cluster of 1 1 mag s tars with one

If

-

c a.t N GC 7 2 2 6

are jus t res o lved at x1 05 but appear rather nebulous at x6 5 .

145

LIST O F ADDITI ONAL OBJECTS . the li s t o f addi t i onal ob j ect s we have inc.luded a number of NGC clusters a s wel l a s number o f small groups and obj e c t s i ated wi th. nebul o s i ty . Als o t o b e found i s NGC 5 6 3 7 , whi ch, gh l ocated b:low the declinati on l imi t of thi s Handbo o k , i s �., tho uthe l e s s an obJ e c t of intere s t . r �e In

�.

m RA D e c; AD Type Con 1 0.0 111 2 p Cep 00 00 . 7 +67 1 6 The bri ghte s t probab l e member of thi s c luster i s BD+ 6 6 ° 1 67 5 , V = 9 . 05 .

2.0 11 2 p 00 3 0 . 1 +6 1 2 3 Contains 40 to 50 s tars be tween 1 3 and 1 8 mag. 4 st

Cas

5.0 I 2 p Cas 00 43 . 6 +64 1 5 The bri gh t e s t probab l e member of thi s c lus ter i s BD+ 6 3 ° 8 9 , V = 9 . 50 , a po s sible H � emi s si on s tar . 0 1 1 0 . 7 +62 1 2 Contains s tars of

11

2.0 t o 1 3 mag.

IV 1 p

Cas

21

8.1 6.0 IV 2 p Tri 01 48 . 7 +27 07 Group of 1 5 s tars ; doubtful whe ther i t i s a c lus ter.

10

4.8 02 1 7 . 0 +58 1 2 Per No type has been as si gned t o thi s group . Contains s tars from 1 1 . 1 7 mag and below, the maj ori ty being o v-er 1 3 mag. Cas IV 2 P 4.5 02 27 . 8 +60 3 2 Contains about 1 2 s tars inc luding an emi s si on�line s tar as sociat ed wi th nebul o s i ty .

i1ng

4

Be le '\le 1 605

02 33 . 9

3.0

+58 53

II 1

P

Cam

Cam 5.0 I 2 P 02 37 . 1 +60 1 8 The bri gh t e s t pro bable member of thi s cluster i s BD+ 5 9° 524 , V = 1 0 . 7 9 1 1 .2 0 4 1 6 . 9 + 58 1 4 Contains about 40 s tars . 04 3 3 . 2

+45 1 2

1 1 .0

5.0

5.0 0 5 2 6 . 0 +34 2 4 Contains s tars o f 9 mag and below. 05 4 7 . 1

+0 7 2 3

3.0

II 1 r

Cam

III 1 m

Per

I 2

P

Aur

III 2 p

Ori

1 46

1 47

Li s t of Addi tional Obj ec t s .

Li s t of Additional Obj ec t s . Cluster

Dec +24 00

m

2 1 57

RA 06 0 3 . 4.

NGC 2 2 3 6

06 28 . 3

+06 5 1

1 1 .4

NGC 2243

0 6 28 . 8

-3 1 1 6

10.9

NGC 2 2 52

06 3 3 . 6 +05 2 4 8.0 7.0 IV 2 p Contains about 1 0 st ars of 9 mag and below .

IC

5

Tr

1 10

06 37 . 1 +02 03 1 0.6 Contains about 6 0 st ar s .

Cr

115

06 45 . 2 +02 03 9.0 Contains about 3 0 st ar s .

Cr

1 32a,b

Ha

8

Tr

6

HI

2 p

HI

2 p

I

12.0

Man

III

1 m

Man

III

2 p

Man

Type AD m Dec 1 .1 I 3 pN 07 5 1 . 5 -26 1 0 Contains about 1 8 s tars of 1 1 mag and below.

Con Pup

1 8b

1 .0 II 3 pN 07 5 1 . 5 -26 1 0 Contains about 7 s tars of 1 2 mag and below.

Pup

Il a

19

1 .8 I 3 pN 07 5 1 . 7 -28 23 Contains about 2 5 s tars of 1 4 mag and below.

Pup

If GC

2 482 20

IGC 2489 bp

44

07 09 . 4 +20 3 7 1 .5 Gem A small group near NGC 2 1 74-5 ( s ee Section 1 of the c at al o gue ) . Contains about 1 5 s tars which are immersed i n nebul o s i ty , along wi th NGC 2 1 7 4- 5 , on the Palomar Sky Survey E-print . P art of Gem OB1 .

Ba

21

CMa 07 1 3 . 7 - 3 1 0 3 3 .9 77 . 5 HI 3 p 1 32a has a di st anc e o f about 560 pc and 1 3 2b abou t 3� 0 pc . The eclipsing binary FF CMa (HD 5 5 1 73 ) 7 . 64 - 7�8 4 ; p = 0 . 547 385d , i s a probable membe r o f. 1 32a.

Hac

07 22 . 3 -1 2 1 7 4.2 IV 3 m C ontains about 3 5 st ars of 1 2 mag and below. 1 0. 0 07 2 5 . 0 -24 1 5 Contains about 2 2 st ars. .

6.5

HI

2 p

NGC 2 3 9 5

07 2 5 . 7 + 1 3 38 9.3 1 5.0 III 1 P Contains about 5 3 st ars of 9 mag and below.

N GC 2 420

07 3 6 . 9

+21 38

9.8

4.0

NGC 2455

07 47 . 9

-21 1 4

10.1

6.0

Ha

0 7 5 1 . 4 -26 1 0 P o s s i bly not a real clus ter.

1 8c

t er 1 8a

2 r

06 3 5 . 4 +09 28 1 0. 0 7 .0 H 3 r Man A probab l e member of thi s cluster i s the red c arbon s tar V 4 9 3 Mon

Cr

N GC 2 1 7 5 s

Type

I

HI HI

2

P

2 p

1 p

CMa pup GelD GelD

pup

puP

RA

07 5 3 . 9

-24 1 4

8.8

1 1 .0

1 .8 07 5 5 . 0 -30 1 2 Contains s tars of 1 4 mag and below. 07 5 5 . 2

-30 00

9.2

8.5

IH

1 m

Pup

II

3 p

Pup

H

2 m

Pup

5.0 III p Pup 07 58 . 1 -28 2 3 Contains about 1 00 OB s tars of 1 2 mag and below. Thi s cluster and the H a 18 groups are probably part of a di s tant spiral arm whi ch i s si tuated at about 6 . 8 kpc from the Sun . 08 00 . 1 -26 58 1.1 11 1 p Pup Contains stars of 1 5 mag and below. Thi s c luster shows l ow reddening whi l e Ha 20 i s hi ghly reddened , i ndicating the tendency of the inters tellar dus t to l i e below the galac tic plane in Puppi s . IH

2533

1 p

Pup

Hac.

08 06 . 0

2548

Hya

lac

08 1 2 . 4 -05 43 5.2 54 . 0 I 2 m C ontains about 1 30 s tars from 9 to 1 3 mag.

257 1

08 1 7 . 9

-29 40

7.4

25 87

08 22 . 3

-29 2 5

9.2

26 27

08 36 . 2

-29 51

8.5

5 36 7

Cen 1 3 56 . 2 -39 51 NGC 5 3 67 i s a refl ec tion nebula in whi ch l i e s a young cluster associated wi th the head of cometary gl obule 1 2 . One of the two mo s t luminous stars i s p o s sibly connec ted wi th the transient X-ray sourc e A1 3 5 3-40. NGC 5367 may li e inside an H I loop , and s t ar formation may have been tri ggered by a supernova explo sion about 1 0 7 yr ago . Absorption 1 magni tude .

Hac lac

Hac

-29 4 7

10.1

1 1 .0

IV

II

HI

1 p

Pup

P

Pup

2 p

Pyx

1

1 48

1 49

Li s t of Addi ti onal Obj e c t s .

L i s t of Additi onal O b j ec t s .

Cluster IC 1 2 57

RA Dec m AD Type 1 7 2 5 . 8 -07 02 Class ifica tion unc ertai n . No data avai l abl e .

Tr

1 7 34 . J -33 2 6 9.1 8.0 I 2 p A heav� ly redden ed young cluste r c ontain i ng d blue super gi ant s t ars . The extin c tion acro s s r h fac e of the c lus ter vari e s from 3 to 8 magn i tud

27

RA 2 1 00 . 2

�

SCa aJl d

:s .

NGC 6469

1 7 51 . 4

NGC 6 5 20

1 8 0 1 . 9 -27 54 7.2 6.0 I 2 m S� A young c lus ter inc luding three s t ars whi ch i l luminat e a refle c ti on nebul a. Two of the star the nebulo si ty are heavi ly reddene d , and the me l. n absorpti on i s 0 . 37 magni tude s .

-22 2 0

12.0

III

2 p

�

NGC 6 540

S�

1 8 04 . 8 -27 49 14.6 Contain s about 2 0 s t ars .

0.5

NGC 6 546

1 8 05 . 7 -23 1 9 8.5 Contains about 45 s t ars .

12.0

III

2 m

Sgr

,NGC 6 58 3

18 14.3

-22 09

1 1 .9

2.5

Il

1 m

Tr

33

1 8 23 . 3

- 1 9 42

9.0

5.0

Il

3 m

Sgr

Tr

34

1 8 38 . 5

-08 3 1

1 1 .6

8.0

Il

2 m

Ro s

Biur Be

Be

4

2 86

87

III

1 p

Dec +68 04

m

AD 5.0

Type

Con Cyg

10.0

Cyg

6.0

Cyg

13

2 1 1 0 . 1 +46 2 2 C ontains about 1 00 s t ars .

12

2 1 1 0 . 4 +45 54 Contains about 75 s t ars .

14

12.0 Cyg 2 1 2 1 . 7 +44 34 Contains about 1 07 s t ars and i s probably a smal l s tar cloud and no t a s t e l l ar group .

15

2 1 2 2 . 6 +48 1 0 Contains 46 probable members , the maj ori ty being c onc entrated in an area of 36 s q . arcminute s .

Cyg

lOO

7067

HOC

71 2 9

1 . 25 1 1 .3 21 40 . 7 +65 59 Cep Contains about 7 s t ars and as s o c i ated nebul o s i ty .

1 9 43 . 2 +27 42 �l A small cluster of 7 or 8 faint s t ars embedded in the dark nebula Lynds 8 1 0 . The main part of the c l oud i s about 1 0 ' x 7 '

la

5 1 46

2 0 02 . 3 +29 00 No data known about thi s c luster exc ept that it p o s s i bly connected wi th I C 4 9 54-5 , a reddened refl ecti on nebula.

Cyg IV 2 pN 9.5 8 .3 2 1 52 . 2 +47 09 A clus ter o f about 1 2 s t ars connected wi th the bri ght and dark nebulo s i ty known as the Cocoon Nebula. The to tal mas s o f as sociated dus t i s about 4 . 5 M O .

Be

94

20 08 . 3 +35 2 4 13.0 Related to nucl eus of Cyg 0131 .

III

2 p

2 0 1 9 . 3 +38 3 6 I 3 p 8.0 The bri ghte s t probable member o f thi s cluster i s HDE 22896 9 , V = 9 . 50 .

Sgr

Set

�l

is

Cy g

Cyg

Cyg

2 0 2 0 . 6 +37 1 6 IV 2 p 8.0 The bri gh t e s t probable member of thi s cluster i s HDE 2 2 90 5 9 V = 8 . 7 0 . The vari abl e V 439 Cyg m re . ( 1 2�6 - 1 3 . 0 , p = 260d) l i e s ne ar the cluste r c e nt

37

IGC 74 1 9

21 23.3

+47 54

1 3.0

2.5

Il

2 p

Cyg

Cep 11 3 m 50 . 0 5.1 2 1 38 . 3 + 57 22 Nuc leus of Cep 0132 . Contains about 30 s t ars , a number showing emi s s i on-lines , and is as sociated wi th the bri ght and dark nebul o s i ty IC 1 3 96

I 1 p 4.0 2 2 2 1 . 8 + 5 5 43 Thi s c luster is obscured by 2 magni tude s .

L ac

Cep 11 3 r 2.5 13.1 2 2 53 . 3 +60 42 Contains the infrared s t ar IRC+60375 , an M7 super­ gi ant . The c luster i s obscured by 4 . 5 magni tude s .

ling

10

II 3 m 3.0 2 2 54 . 4 + 5 9 02 Contains a number o f emi s s i on-l ine s t ars .

li ng

20

2 3 32 . 1

12

I 2 2 .0 23 5 1 . 8 + 6 1 49 Contains about 27 s t ars from 1 0 to 1 6 mag .

+ 58 2 2

5.0

Il

Cep

1 p

C as

P

C as

1 51

PART FOUR

A CATALOGUE OF GLOBULAR CLUSTERS .

o gue contains obs ervations of 6 3 globular c lu s t ers TIl e catalobs ervers using t e l e s copes of 40 to 3-inches aperture 1 1 by ,.a e 80 , 20 x 50 and 7 x 35 binoculars . The obs ervations are x 5 1 -ai d ed int o two sec tions c om � ri sing a ) descripti ons and field c lus ters and b ) d e scriptions of a further 1 0 ��Win gs of 53 no field drawings are avai l able . Di s tribution ch whi for cts catalogue i s as fo ll ows . the thin wi a a.t Il s i d e s of the l eft-hand page s show the Webb left xtreme T e e ogue number ( WS ) , thes e continuing in numeri cal catal y t � ie uence from the las t entry in the c atalogue of open c lusters p ar t Three . Each Webb Soci ety number is followed by the � tua.l desi gnation of the c lus ter whi l e for tho s e clus ters whi ch �. Me ssie r obj e c t s the Me s s i er number wil l appear below the rel evan t NGC number . The remaining dat a , covering the greater parts of the l eft­ UDd page s , i s as follows .

� :; :

:

:

!Her Line . ( a ) posi tions for 1 97 5 . 0 (b) V magni tude s of c lus ter s (m ) , ( Kukarkin 1 97 4 ) . ( 0 ) Angul ar diame ters of clus ters in arcminutes (AD ) . All of the diame ters are pho tographi c measure s ( Alcaino 1 97 3 ) . (d) Concentration c l as s e s o f clust ers ( Con Cl ) , ( krp 1 96 5 ) .

(e) The abbrevi ated form of the rel evant c onstell ati ons (Con ) .

In a number of cases addi ti onal information wi ll be found b e low the data di splayed on the upper line . !lrual Obs ervati ons .

Th data below the dotted lines are c ontrac t ed renderings of ob s erve ati ons from the Webb Soci ety fi l e s . The observations are t ou t in order of decreasing aperture , the fi gure s in parenea i a , (40) ( 8 ) e tc . , are the re spec tive aperture s in inche s . quote d magni tude s , di ameters e tc . are purely eye e stimat e s . t re obs ervati on s made by more than one person using identi c al e 1 t s cop e s are concerned , the re sul t s have been run toge ther o a s ingle sec tion . Drawings . T ob h e se wi l l be found on the oppo s i t e page s to the relevant e rVat i ons , and c ons equently number four to a page . All the �ings are shown in circ l e s of 57 mm diameter , regardl e s s o f actual fi eld diameters in arcminute s . Ori entation i s north e ast to the right .

� �l � : � �

1 53

1 52

A Catal ogue o f Gl o bular Clu s t ers .

A Catalogue of Globular Clus ters . L i s t of Obs ervers . The following l i s t shows ·the names of the obs ervers wh o se appears in the catalogue , plus detai l s of their locations and 'No !'k respective telescope s . 60-inch D . A . AlIen . Ten eri ffe , Canary I sl an 40 Cerro las Campana s , C h ilds . e . 1 2 o . g. Cambridge , U . K . " It 8t " It 8 J . P erkins . 18 Che s terfi eld , U . K . " P . Andrew . " 18 M . J . Thomson . 1 6� Santa Barbara, U . S . A. It It " 8 , 6 o . g. S . Selleck. 1 S . J . Rynes . Wi staston , U . K . E . S . Barker . 8� Rerne Bay , It C . Nugent . 8t Pontefrac t , " K . Glyn J one s . 8 Winkfi eld , " " K . Sturdy . 6 Relmsley , D . Branche t t . 3. Bi shops toke , " Binoculars . D . A . Allen . 7 x 35 D . Branchet t . 1 5 x 80 , 2 0 x 50 . Obs ervers and Accredi ted Clus ters . The following l i s t shows all the globular clus ters that are featured in the first section of the catalogue ( wi th field drawings ) plus the ini tials of the re spec tive observers . Clust ers are li sted in catalogue order , i . e . , in order of RA . NGC 1 904 MJT , S S , KS . NGC 6 2 3 5 MJT , SS , DB . 2 4 1 9 MJT , DAA , JP . 62 54 MJT , SR , S S . 4 1 47 MJT , DAA , SS , DB . 6266 KGJ , DB . 4590 KGJ , S S , KS , DB . 6 2 7 3 DAA , KGJ , SS , DB . 5024 DAA , S S , KGJ , KS . 6284 S S , DB . 5053 MJ T , DAA , SS , DB . 6287 S S , DB . 5272 MJ T , SR , S S , KS . 6 3 2 5 S S , DB . 5466 MJT , SS , DB . 6341 J P , PA , MJT , SR , KS . 5 6 34 MJ T , DAA , SS . 6333 DAA , S S , SR . 5897 MJT , SS . 6 342 SS , DB . 5904 DAA , MJT , KGJ . 6 3 56 DAA , SS , DB . 6093 DAA , S S , ESB , SS , DB . 6402 DAA , KGJ , KS . 6 1 2 1 MJT , SS , SR , DB . 6401 SS , DB . 6 1 44 MJT , DAA . 642 6 S S , DB . 6 1 7 1 DAA , S S , DB . 6 5 1 7 SS , DB . 6205 JP , PA , DAA , SR , KGJ , KS , DB. 6 5 3 5 MJT , S S , DB . 62 1 8 MJT , DAA , KGJ , KS . 6539 S S . 6229 MJ T , DAA , ESB , DB . 6626 MJT , SR , KGJ , S S , J{S .

�i

N GC 663 8 663 7 66 56 668 1 67 1 2 61 1 5 67 60 61 7 9 68 09

MJT , S S . SR , S S . DAA , SR , KGJ , S S . KGJ , SS , DB . MJT , SS , KS . KGJ , SS . MJT , DAA. MJT , KGJ , KS . SR , KS .

DAA , SR , K S . DAA , KGJ . MJ T , S S , DB . MJT , KGJ . MJ T , SR , KS . DAA , MJT , KGJ . SR , KGJ , KS . CN , KGJ , KS , DB .

NGC 6838 686 4 6 9 34 6981 700 6 7 01 8 7 089 1 099

s t ers for whi c h no ! i el d B ? low are shown the glo bular cluform the secon d s e c t l on of which and e l ab l avai dr awl n s 1 a although below the ch whi , en C s e i � clude W the a a o 1e 1� m The tri king obj e c t s a is , k o Handbo s thi o of t O l � t lon ... 1 de cl lna Wl. th th e al c l dent t is i wo rthy of inclu sion . The forma pr ec edi ng l i s t . NGC 6,3 1 6 S S . 28 8 DAA. NGC 6355 SS. . T rU , DAA 5 1 39 6 3 66 s s . 5694 S S . T'IJ T , S S . 6440 6 2 9 3 SS . T. MJ 6642 6 304 SS .

� �

0

0

A Catal o gue

l'a.rt One

of

Glo bular C lus ters .

155

Descriptions and Fi eld Drawings of 53 Glo bular Clus t ers .

1 57 1 56

WS 367

Cat NGC 1 904 M79

RA

m 7 . 84 Bri ghte s t s t ars 1 4 magI - - - - - - - - - 05 2 3 . 2

Dec -24 3 3

AD

7 .8

Con Cl

C on

V

( 1 6� ) Extensive core ; many bright members on at HP ; easy to res olve .

Lep f.

s i de

( 8 ) Outer areas reso lved x241 , more s o to th e N . ( 6 ) Smal l , nebulous ; bri ght , non- s t el lar cen tr e . 368

NGC 241 9

07 3 6 . 5

+38 57

1 0 . 80

•

if·

•

---

6.2

II LYn Very di s tant obj ec t ; fi gures range from 61 to 83 kpc -

-

-

NGC 1 904 - M7 9 a-ineh x1 00

( 1 6� ) Irregularly round wi th bri ght c entre ; no s i � of res olution to x3 3 3 , but c luster shows mott lin g.

NGC 2 4 1 9 8-inc h x65 Fi eld 5 5 '

Field 4 0 '

( 1 2 ) 2 ' diam . ; faint and not we ll c ondensed. ( 1 0 ) Faint haze wi th s l i ghtly bri ghter c entre , th e

lat ter showing signs of mot tling x1 3 2 . 369

NGC 4 1 47

1 2 08 . 9

+18 41

1 0.28

4.1

VI

Corn

I.

Glyn J one s

P . Brennan

( 1 6� ) Bri gh t nuc l eus ; fades s l i gh tly at edges wh ich

are just resolvable on

MP .

( 1 2 ) x80 2 ' diam . ; fairly c onden s e d . ( 8 ) Bri ghter c entre ; s t ar s e en o n N . p . edge . ( 1 5 x 8 0 ) Very faint , smal l oval ; elusive obj ect . 370

-2 6 3 7

8.5

x

Hya

NGC 4590

1 2 38 . 1

M68

S tars 1 2 mag and below. - - - - - - - - ( 8 ) Round di sc about 4 ' d i am . wi th arc s of bri gh t er s t ars in the S and W regi on s ; orange s tar abou t 5 ' NW of c entre ; x2 96 wel l-re solved , but a haze of unreso lved s t ars s ti l l evi dent . ( 6 ) 4 ' diam . , unre solved ; too low for HP.

9.8

( 3 ) Faint , l arge oval haz e ; unre so lved x40 .

NGC 4 1 4 7 8-inc h x40 Fi eld 80 '

NGC 4590 - M68 8-inc h x40 Fi eld 6 5 '

K . Glyn J ones

159 1 58

WS

3 71

Cat NGC 5024 M53

RA Dec m AD Con Cl 7 . 71 14 . 4 1 3 11 . 7 +18 18 V Bri ghtest star s 13 . 8 . Very old clu s ter . - - - - - - - - - - - - - - - - - ( 12 ) Bri gh t , 'veakly resolved ; 3 ' diam .

Con

-

COI'll -

(10) Very compres sed ; x148 edge s reso lved an d s t ar s qui t e scatt e re d ; x44 5 resolution at c entre . ( 8 ) Bri lliant nucl eu s , about 2 ' di am . , surrounde d by a halo o f l i gh t ; takes moderate magni fi cat i on . ( 6 ) Fine obj e c t ; parti ally resolved x12 0 . 372

NGC 5 0 5 3

1 3 1 5 . 1 +17 48 XI Low lumino s i ty c lu s t e r ; 3 , 400 star s t o 21 mag.

-

C om -

- -

( 16! ) x7 0 diffu s e spo t wi th few s t ars resolved ; still sparse but c omple tely re so lved x22 2 , x3 3 3 .

NGC 5024 - M53 8-inch x100

P . Brennan

( 1 0 ) Bes t at LP ; a few s t ar s s e en at c entre x2 96. (15 x 8 0 ) Very faint , small oval . M3

13 41 .1

+28 3 0

18 . 6

Contains s t ar s o f 12 . 4 mag and below. - - - - - - - - - - - - - - - -

CVn

VI -

Field 5 0 '

Field 4 0 '

( 12 ) x2 5 0 very diffi cul t ; 2 ' diam .

3 7 3 N G C 5272

N G C 5053 8-inch x6 5

-

( 16�) Core resolved x2 22 ; p . side appe ar s ri che r due p o s si bly to dark bay in S . f . regi on . ( 8� ) Just reso lved x154 ; blui sh tinge suspec ted. ( 8 ) Very compac t and much bri ghter at the cent re ; beautifully resolved almo s t to the middl e .

x1 2 1

( 6 ) Granul ar a t HP ; c entre not res o lved .

------

3 7 4 NGC 5466

BoO 9.2 XI I Contains s t ar s of 15 mag and below. - - - - - - - - - ( 16!) Lacks c entral concentration and i s comp l e t elY

14 14 . 3

+28 3 9

9 . 35

-

reso lved x16 0 ; not rich in s t ars . ( 8 ) Large but faint ; some resoluti on x121 ; diffi cu l t . ( 1 5 x 8 0 ) Faint , opaque c l oud ; easily overloo ke d .

NGC 5272 - M3 8-inc h x100 Fi eld 40'

NGC 5466 8-inc h x65 Fi eld 5 0 '

P . Brennan

161 160 WS

375

376

Cat NGC 5634

NGC 5897

Dec -05 5 2

m 9 . 58

AD

Con Cl Con IV ViJ:' - - - - - - .. ( 1 6! ) No t t l ed x1 60 ; outer areas resolved x22 2 . ( 1 2 ) x2 50 barely reso lved edge s ; n o t much con d en Sed ( 1 0 ) x44 5 entire c luster mottled ; very c ompac t . RA 1 4 28 . 3

3.7

.

•

8 . 59 1 5 1 5 . 9 -20 5 5 XI - - - - - - - - - - - - - - .. ( 1 6!) Only s l i ghtly bri ghter in the middle ; many f ai n t s t ars vi sible x70 ; l acks any bri gh t member . ( 8 ) Pre t ty bri ght and large ; s ome re s o lutio n x 1 45 . �

377

NGC 5 904 M5

15 17.3

+02 1 1

C ontains s t ars o f 1 2 mag and below. - - - - - - - - - - - - - -

V

Ser

�

-

- - - - - - ( 60 ) 1 2 ' di am . ; l o o s e obj e c t which i s well-re solved almo s t to the middle . -

�.

- ..

of s tars to the S ; magnifi e s wel l . 378 NGC 6093 N80

Fi eld 50 '

P . Brennan

( 1 6�) Exc eedingly bri ght ; l arge central area with a brigh t s t ar almo s t at c entre ; x7 0 outer ! resolved �d further magni fi cati on fi l l s the fi e l d of vi ew. ( 8 ) Curve s of s eparate s tars t o the N and little

NGC 5897 8-inch x6 5

NGC 5634 8-i nch x6 5 Fi eld 50 '

knots

Seo 7 . 31 -2 2 5 6 II 5.1 Contains s t ars o f 1 3 . 7 mag and below. 6 . 5 mag nova se en in 1 86 0 . Extens i ve nebulo s i ty c l o s e b y thi s c lu ster . - - - - - - - - - - - - - - - - - - - - - - - - -

1 6 1 5.6

( 1 2 ) 4 ' diam . ; bri ght and well-conden s e d . ( 1 0 ) Smal l , c ompac t ; outer parts reso lved at NP . ( 8!) Bri gh t , almo s t s te l l ar nucl eus ; s t ands high magni fi cati on wel l , but only shows mo t t l ed ed ge s . ( 6 ) x 1 83 s l i gh t resoluti on at the edge s and wi th x30 5 t o x45 7 qui t e goo d resolution obtained . ( 1 5 x 8 0 ) Just i denti fiabl e .

NGC 5904 - M5 8!-inch x204 Fi eld 1 2 '

NGC 6093 - M80 8-inch x40 Fi eld 6 5 '

K . Glyn J ones

1 63

1 62 WS 379

Cat NGC 6121 M4

RA Dec m AD Con Cl Call. 1 6 22 . 1 -2 6 2 7 5 . 96 2 2 .S IX SCo Bri ghtest s tars 10 .S mag. In regi on of Ant ar es moving clus t e r . - - - - ( 16t) Exceeding ly rich wi th hi ghly c oncen tr a t ed c entre ; resolves wel l at HP . -

�

�

( 1 0 ) Wel l-re s olved at powers from x59 to x2 9 6 ; at the centre a line of s tars N . f . - S . p . (st ) Bri ght c luster s t ars lie i n 2 c onverging band

the N-S one containing at least 2 pairs . ( 3 ) stars scattered around the edge s . 380

NGC 6144

16 25.7

-2 5 49

9 . 07

6.2

XI

-

Sea

�

s, -

- - ..

( 16t) Mottled background wi th a few s tars re solved . (12 ) x80 l ' diam . ; very diffi cult obj ec t . 381

382

NGC 6171 M107

NGC 6 2 0 5 M13

1 6 31 . 1 - - - -

-12 59

S . 17 - - - -

-

7 .S

X

-

( 1 2 ) xSO 3 ' di am . ; unresolved . (S ) x145 r e solved t o the centre ; suspec ted dark ( 3 ) Faint , elusive opaque haz e .

Oph -

( 6 ) x1 30 fully resolved ; lanes of s tars from (10 x 50 ) Bri ght , compac t nebular haz e .

8-inch x40

S-inch x6 5

Field 6 5 '

Fi e l d 4 5 '

P . Brennan

- -

area.

Her 16 40 .S + 3 6 3 0 5 .s6 v Bri ghte s t s t ar s red gian ts of 12 mag. Over 30 , 0 00 s tars t o 21 mag. Total number of s tars about 1 mi ll ion . - - - - - - - - - - - - - - - - - - - - - - - - - . ( 1S ) Wholly reso lved wi th very crowded cent re ; many g. yellow stars , and three-dimensi onal effect ve ry s tron ( 12 ) 1 0 ' diam . ; s everal hundre d s tars resol ve d . ( S�) x154 cl oud of tiny s tars wi th bri ghte r on e s interspersed ; nucleus about 4 ' di am . ; no col our s . ( S ) Sli ghtly flattened on E side ; magnifi e s we l l and

i s resolvabl e practical ly to the centre .

NGC 6144

NGC 6121 - M4

N to

SE.

NGC 6 2 0 5 - M13

NGC 6171

8-inch x100 Fi eld 40 '

8-inch x6 5 Fi e ld 5 0 ' K.

Glyn J ones

1 64 ws

383

Cat NGC 62 1 8 M12

RA Dec m AD Con Cl Con 1 6 4 5 . 9 -01 5 5 6 . 88 12.2 IX ° ph Contains s t ars of 1 1 mag and below. - - - - - - - - - ( 1 6! ) Core l arge and very bri ght ; x7 0 oute r ar e as reso lved into many small s t ars . ( 1 2 ) 5 ' di am . ; just resolved at the edge s . ( 8 ) Easily re solve d ; outline far from c i rcular the slightly denser centre flat t ened to the SW. -

-

-

-

-

-

( 6 ) Partly resolved ; two short l anes on p. sid e . 384

NGe 6 2 2 9

1 6 46 . 3

+47 3 4

--­

3 .8

IV Her ( 1 6!) Bri ght , small and round ; c en tral area almo s t s t e l l ar x7 0 ; not easily resolve d , x 3 3 3 sho\vin g it to be mottled wi th just a few faint s t ar s vi sible . ( 1 2 ) x80 faint and unreso lved ; 2 ' di am . -

-

-

-

-

-

..

I.

( 2 0 x 5 0 ) Faint , small oval blo b . 385

NGe 6235

1 6 5 1 . 9 -22 07 - - - - -

IV

NGe 621 8 - M1 2 8-inch x40 Fi lild 6 5 '

Glyn J ones

NGe 6 2 2 9 8t-in ch x1 02 Field 2 4 '

E . S . Barker

Oph

( 1 6!) Small , pretty bri gh t ; no res o lution . ( 1 0 ) Faint , s l i ghtly bri ghter towards the centre at x59 ; x296 s l i ght resoluti on . ( 3 ) Very faint , smal l and di fficul t . 386

NGe 6 2 54 M10

O ph -04 04 12.2 6 . 63 VII Bri ghtest s t ars 1 1 . 6 mag. No RR Lyrae s t ars and few o ther vari abl e s are in thi s cluster. - - - - - - - s ( 1 6!) Very bri ght core ; x70 numerous s t ars on t h e e dge and x 1 6 0 a l arge number of bright s t ars in th e c e nt re ; x2 2 2 dark s tarle s s regi on s on the S edge of c en tr e . of ( 8!) 1 0 ' di am . ; c entral 4 ' nebulous at LP ; a numb e r s t ars resolved x 7 7 and well-re s olved x1 54 . ( 6 ) x457 resolved in c entre ; c ompac t and even a t �.

16 55.8

-

-

-

-

-

.

NGe 6 2 3 5

NGe 62 54 - M1 0

8-inch x6 5

8-inch x1 00 Fi eld 40'

Fi eld 4 5 '

K . Glyn Jones

1 66 ws

387

Cat NGC 6266 M62

Dec RA m Con Cl COll. 6 . 53 1 6 59 . 7 -30 05 IV Sco The SE regi on of thi s clus t er is o bs cure d by a d c loud (Ay = 0 . 7 5 mag) rel ative to the NW re gion . 1l.st - - - - - - - - - - - - - -

-

-

-

,

( 8 ) Smal l , very bri ght wi th a s l i ght blui s h gl ow. condensed portion to SE of c entre wi th s tars f �, . 1Il0S! l. n g out to the NW , giving a c omet-like look; mod e r at e magni fi cation resolves all but the SE part . ( 3 ) Bri gh t , fans out in al l direc t i on s . "

388

NGC 6273 M1 9

,

---... 1 7 01 . 0 -26 1 3 6 . 83 VIII Oph - - - - - - - - - - - - - - - ( 1 2 ) 4 ' diam . ; elongated N-S ; edge s barely res o lved, ( 8 ) Edge s fairly easily re solved on MP ; about 10 t o 1 5% longer N-S than E-W; x241 very well resol ved with edge s qui te s traggling; does not s tand use of high -

-

..

NGC 6266 - M62 8-inch x2 00 Fi eld 2 0 '

powers from mid-northern lati tude s . ( 3 ) Very bri ght oval wi th s tars scattered on edges. 389

NGC 6284

NGC 627 3 - M1 9 8-inch x40 Fi eld 6 5 '

K . Glyn J ones

2.7 1 7 03 . 0 -24 43 IX 9 . 03 Oph - - - - - - - - - - - - - - - - - - - - - - ( 1 0 ) x59 qui t e compac t , spheri cal and bri ghter towards the c entre ; edge s ill-defined . x1 48 s l i ghtly resolved and well-resolved at x445 . ,

( 3 ) Bri ght oval wi th edge s fanning out . 3 90

NGC 6287

Oph 1 7 03 . 6 -22 40 9 . 44 VII n Brightest s tars 1 5 . 4 mag, Thi s c lus ter lies in a r egi o of dark nebulo si ty connec ted wi th the Antares mo ving c luster. Absorption i s over 2 magni tudes . - - - - - - ( 1 0 ) Pre t ty bri ght , c ompac t and spheric al x59 ; x 1 48 and x2 96 suspected re solution around edges . ( 3 ) Bri ght oval nebul o si ty . -

-

-

-

-

-

-

-

NGC 6 2 8 4

NGC 6287

8-inch x1 2 5

8-inch x7 5

Field 2 8 '

Fi eld 40 '

P. Brennan

1 69 1 68 WS 391

Cat NGC 6 3 2 5

392

NGC 6 3 4 1 1192

Con Cl AD m Dec RA 1 .6 1 0.73 1 7 1 6 . 5 -23 44 X - - - - - - - - - - - - - - - - - - - - ( 1 0 ) x59 faint and s l i ghtly bri ghter towar ds th e centre wi th i l l-defined edge s ; x1 48 and x2 96 S l i gh t trac e s o f resoluti on . ( 3 ) Very faint and smal l ; elusive obj ect . +43 1 0

6 . 50

12.2

IV

-

-

-

--­ Her

( 1 8 ) To tal resoluti on wi th the c entre a kno tty m as s o f s tars wi th overlaying bri ghter one s ; The N . edge much flatter than the irregulari ty o f the rest .

( 1 6! ) Exc eedingly bri gh t c entral regi on wi th the E edge richer in faint s t ars ; x2 22 dark areas on the E side be tween the core and a line of s t ars ; between lines of s tars running SW to E i s a l arger dark area. ( 8! ) x7 7 resolved around periphery ; x 1 54 2 ' nucl eus a t the c entre of a swarm of s t ars of 1 2 mag and below;

NGC 6 3 2 5 8-inc h x65 Fi eld 5 5 '

NGC 6 3 4 1 - M92 8t-inch x2 04 Fi e l d 1 2 '

E . S . Barker

s everal s t ars re s o lved in the nuc l eus .

( 6 ) Bri ght nuc l eus and many outli ers ; f . side fainter. 393

NGC 6 3 3 3

17 17.7

M9

The bri gh t e s t s t ars in thi s c luster about 1 3 . 1 mag. - - - - - - - - - - - - - - - - - - - - - -( 1 2 ) x80 5 ' di am . , qui t e bri ght , moderately cond en sed .

-18 30

7 .75

VII I

Oph

( 1 0 ) Very compr e s s ed x59 ; beauti fully re s o lved x44 5 . ( 8� ) About 7 ' di am . ; outer areas re s o lved o n MP .

-

3 94 NGC 6 342

Oph 1 7 1 9 . 7 -1 9 3 3 10.10 IV - - - - - - - - - - - - ( 1 0 ) x59 smal l , fai rly bri ght and uni form ; x2 9 6 i s s l i ghtly resolved and po s si bly not ci rcular . ( 3 ) Faint but easily s een on c l ear ni ght s .

-

N GC 6342

N GC 6 3 3 3 - M9 8-inc h x1 00 Fi e l d 40 '

8-inch x 6 5 Fi e l d 50'

P . Brennan

171

1 70 ws

395

Cat NGC 6 3 5 6

Dec - 1 7 47

m AD Con Cl 8 . 28 3.5 11 - - - ( 1 2 ) x80 2 ' di am . , uni form brightne s s . ( 1 0 ) x59 c ompact and s pheri c al wi th i l l-de fin e d RA 1 7 22 . 2

-

-

-

-

-

-

x2 9 6 resolution of outer s t ars . ( 3 ) Bri ght , opaque cloud . 3 96

NGC 6 402 M1 4

e d ges. t

7 . 49 VIII star s of 1 5 . 6 mag and below. A nova o f 1 6 mag a e pp are d in thi s c luster in 1 964 , but may not have been a m emb

-

-

-

-

-

-

-

_

_

_

_

_

_

_

_

_

_

_

_

_

_

_

_

_

_

_

�

er, -

( 1 2 ) x80 2 ' . 5 di am . , qui t e bri ght , moderately c ond en S ed, ( 8 ) Seems fainter than given mag; perfectly round , hazy

patch showing trace o f resolution at the periphery with x1 00 ; no defini t e central c onden s ation . ( 6 ) Nebulous glow partly resolved ; very slight hint of nucl eus ; diam about 4 ' . 397

NGC 6401

NGC 642 6

-

-

-

-

NGC 6402

6356

-

M14

8-inch x1 00 Fi eld 40 '

8-inc h x6 5 Fi eld 4 5 ' K.

? 1 7 3 7 . 1 -2 3 54 1 .0 Oph Thi s c luster obscured by about 2 . 69 mag. - - - - - - ( 1 0 ) x59 qui t e c ompact and spheri c al wi th edges not well defi ned ; x1 48 one or two s t ars s e en towards the c entre; x2 9 6 dark areas suspec t ed . ( 3 ) Smal l , bri ght oval -

3 98

NGC

Glyn J on e s

-

Oph +03 1 1 1 1 . 48 2.2 IX Thi s c luster obscured by a little over 0 . 7 5 mag. - - - - - - - - - - ( 8 ) x48 faint and circular wi th very gradual cen tr al 1 7 43 . 6

-

-

-

-

-

-

-

bri ghtening; x1 2 1 appears to be mo t t l e d and the b ord ers are i rregular . x1 45 , x24 1 a few s t ars noticeabl e . ( 3 ) Faint , smal l elusive obj e c t .

NGC

NGC

6401

8-inch x6 5 Fi eld 5 0 '

6426

8-inch

x65

Field 4 5 '

P . Brennan

1 73 172 ws

399

Cat NGC 6 5 1 7

RA 1 8 00 . 5

Dec -08 57

m 1 0.29

AD

1 .0

Con Cl IV •

( 1 0 ) Faint and small x59 wi th very gradual br i gh t . " , en�ll . towards the c entre ; x445 s ome resolutlon obt ain ed b ut € thi s i s di ffi cul t to achi eve .

:Ji;

( 3 ) Very faint and smal l ; di fficul t . 400

NGC 6 5 3 5

1 8 02 . 6

-00 1 8

1 0 . 62

XI

-

� O ph -

( 1 6�) Small and faint x7 0 wi th irregularly round a few s tars resolved around the edge s , the four bri ghte st being on the W edge . ( 6 ) x1 52 sl i ght resolut i on ; po ssible s tar on the

-

s ha pe.

,

S'P.

edge ; becomes di ffi cult wi th increasing magni ficat ion . ( 3 ) Faint , elusive obj e c t . 401

NGC 6539

1 8 03 . 5

- 07 3 5

9 . 62

X

-

Ser -

- - .

( 1 0 ) Uniform in bri ghtne s s and appears on the verge of resolution x5 9 ; x2 9 6 sl i ght resoluti on to the extent of about five fairly bri ght stars on the edges . 402

NGe 6626 M2 8

P.

NGC 6 5 1 7 8-inch x65

NGC 6 5 3 5 8-inch x6 5

Fi eld 4 5 '

Fi eld 5 0 '

P . Brennan

Brennan

-2 4 5 3 Sgr 6 . 99 1 5.0 IV Bri ghte s t s tars in thi s c lus ter about 1 3 . 2 mag. 18 23.0

- - .

( 1 6� ) Easily resolved x84 ; bright , irregularly round c entre wi th outer parts cons i s ting of a large numb er of small stars ; fine s i ght x1 7 6 . ( 8� ) Small , circul ar nebul o si ty x56 ; not res olve d x 1 1 1 but suspi cion of peripheral resolution x1 5 5 . ( 8 ) Compac t obj ect wi th bri ght , glowing c entre which fades off rapidly towards the edge s . At mi d-northern l ati tudes i t appears smal ler and fainter than expected, and only resolves at the edge s wi th s om e

NGC 6 5 3 9

NGe 6 6 2 6 - M2 8

8-inch x6 5 Fi eld 5 0 '

8-inch x40 Fi eld 6 5 '

difficul ty; from Californi a x2 41 resolve s to tal l Y , ( 6 ) 2 ' - 3 ' diam . ; bri ght , stellar c entre .

K.

Glyn J ones

175 1 74 WS 403

Cat NGC 6638

Dec RA 1 8 2 9 . 4 -2 5 31 - - - - - - -

404

NGe 6637 M69

AD

Con Cl Con VI S gr - ( 1 6�) x3 5 1 wel l-resolved , the maj ori ty of s t ar s being on the NE edge . ( 8 ) Smal l , bri ght wi th a few outer members re so lv ed . V 3.8 7.79 1 8 2 9 . 7 -32 2 2 The bri ghte s t s tars in thi s clus t er are 1 3 . 2 m ag . - outer th wi , l smal and ght ( 8� ) Fairly bri regions a l i t tl e i rregular ; hardly any c entral condens ati on , �d x2 5 0 resolved the c lus ter into faint , evenly-sp ace d s t ar s ; di ffi cul t from mid-northern l ati tudes . ( 6 ) x305 resolved to the centre . -

m 9 . 03 -

2.2

-

-

-

�

-

4 05

NGC 6656 M22

NGC 668 1 M70

-

�

�

5 . 07 1 8 34 . 8 -2 3 5 7 VII 17.0 S gr The bri ghte s t s tars in thi s c lus ter are of 1 1 mag, including one reddi sh o bj ec t . There i s obscuring materi al in the regi on abs orbing by 1 . 72 magni tudes . - - - - - - - - - - - - - - - ( 1 2 ) Well-re s o lved ; very large and bright . ( 8t ) Already reso lved x56 ; elongated E-W wi th wel s tars , including bri ghter one on S edge ; di am . 1 0 ' . ( 8 ) Fine , large object easi ly reso lvable di s tinc t ly non-ci rcular . ( 6 ) x1 52 c lus ter covers the entire fi eld ; contains a knot of s t ars si tuated N o f centre . -

406

-

1 8 41 . 6

-32 2 0

-

8.18

-

-

V

-

Sgr

-

-

�

NGC 6 6 3 8

NGC 6 6 37 - M69

8-inch x65

8-inch x200

Fie l d 4 5 '

Fie l d 2 0 ' K.

Brennan

-

-

-

-

( 8 ) Small wi th sharp central condens ation aro und whi cb i s a fainter area seemingly sligh tly flattene d t o the E ; outer edge s reso lved x2 50 . ( 6 ) Bri ght centre ; edge s re s olved x1 5 2 , x1 83 .

Glyn J ones

NGC 6 6 5 6 - M22

NGC 6681 - M70

8-inch x40

8-inch x200 Fi eld 2 0 '

Fie l d 6 5 '

( 3 ) Very bri ght nebulous cloud . Jones

K.

Glyn J ones

1 77

1 76

WS 407

Cat NGC 67 1 2

RA Dec m AD Con Cl 1 8 5 1 . 7 - 08 45 8.13 4.2 IX The br g t � s t r n t i l s ter are 1 3 . 3 m a g. _ - - -

�� �����

����

-

-

-

�

..

( 1 6t ) Easi ly re solved at LP ; at HP a defin i t e d ark lane be tween the centre and the SE edge ; irr eg ul ar. ( 8 ) Easi ly re s olved x1 2 1 ; x241 po s sible dar k ar ea s . ( 6 ) Moderately condensed and eas i ly resolv ed . 408

NGC 6 7 1 5 M54

---­ 1 8 5 3 . 6 -30 3 0 III S g:r The brigh t e s t s tars in thi s clu s t er are 1 5 . 6 m ag. - - ( S ) Very smal l and bri ght , almo s t like a plan e tary -

-

-

-

-

�

nebula at fi r s t si ght ; s t ands HP wel l , but from m id_ northern lati tude s even x2 50 fai l s to resolv e ; from s outhern Cal i forni a the halo of outer s tars i s very s l i ghtly re s o lved and the c luster i s slightly extended E-W ; one bri ghter s tar on S edge . 409

NGC 6760

1 9 09 . 9

9 . 0S

+00 5 9 -

-

-

-

2.4 - - -

IX -

-

Aql -

-

NGC 67 1 2

NGC 67 1 5 - M54

8-inch x65

8-inch x2 00

Fi eld 5 5 '

Fi eld 2 0 '

K . Glyn J ones

-

( 1 6�) Outer edge s mo ttled xS4 ; x 1 76 bri ghtens very gradually towards the middle whi l e outer edges are s t i l l diffu s e ; x3 5 1 bri ght kno t towards S edge , but no actual re solution obtained . ( 1 2 ) l ' di am . , unre solve d . 410

NGC 6779 M 56

1 9 1 5.6

+ 3 0 08

S.21

X

The bri ght e s t s t ars in thi s cluster are 1 3 . 1

1yr mag .

( 1 6t) Non-circul ar shape ; re solve s complete ly t o t h e core. c entre and c on tains a bri ght s tar near NW edge 0 f h ( S ) Smal l , moderately bri ght and of even den s�" ty wit of no very marked c entral c ondensation ; c entral r e g1" on , " s sioIl, about 4' diam . give s a s l i ghtly three -lobed �m p r e " too faint to t ake hi gh magnification for res o1 u t 1 on· ( 6 ) Irregul ar outline ; parti al re s oluti on x1 2 0 .

NGC 67 6 0

NGC 6779 - M56

S-inch x1 2 5

8-inch x1 00

Fi eld 2 5 '

Fi eld 4 0 ' K.

Glyn J ones

1 79 178 WS 41 1

Cat NGC 6809 M55

Dec AD RA m Con Cl Con 6 . 33 1 4.8 1 9 38 . 5 -3 1 00 XI Sgr The bri ghte s t s tar s in thi s clus ter are 1 1 . 2 ma g. - - - - - - - - - ( 8� ) Very di ffi cult to see from mid-north ern r e�' ."l O ns I. however , i t i s large , and can be re s o lved on MP . , on HP elongat ed N-S wi th an irre gular outlin e ; st ar , S Of about 1 2 mag and below . -

-

-

-

-

-

-

-

-

-

-

-

�

a

( 6 ) Resolved to the centre x68 ; contains qui t e chains of s t ars . 412

NGC 6838 M71

-

-

-

-

nuc l eus ; certain degree of granulari ty wi th a po s sibly re solved ; poor image at HP . ( 6 ) Nebul o s i ty conc entrat ed in W oart . -22 00

8 . 52

I

NGC 6864

20 04 . 7

M7 5

The bri ghte s t s t ars in thi s clus ter are 1 5 . 6

An

-

( 1 2 ) x80 4 ' diam . , just resolved . ( 8�) Low surface bri ghtne s s and no indic ation of

41 3

f ew

8 . 28 6.1 ? 1 9 52 . 6 + 1 8 43 The bri ghte s t s tars in thi s clus ter are 1 2 . 0 mag . Algol-type eclip sing variable i s a member . - -

"

-

.

NGC 6809 - M55

NGC 6838 - M7 1

8-inch x200

8-inch x1 00

Fi eld 2 0 '

Fi e ld 40 '

a

K . Glyn J ones

Sgr mag.

( 1 2 ) x80 2 ' di am . , bri ght but unresolved . ( 8 ) Compac t , about 2 ' - 3 ' diam . wi th bri ght centre of about l ' in si z e ; x 1 2 0 a slight mot tling of the edges s e en ; higher powers not sati sfactory from a latitude of 5 1 tO N . 4 1 4 NGC 6 9 34

2 0 32 . 9

+07 1 9

6.2

VIII

Del

( 1 6� ) x7 0 mo t t l ed , e speci al ly on the S side , and th1' S and the E edge resolved at x 1 6 0 ; at HP the W s i d e shows negligabl e resolution , unlike the res t . ( 8 ) Parti al resolution to x362 . ( 1 5 x 8 0 ) Faint , small oval di sc .

N SC

6864 - M7 5

NGe 6 9 3 4

a-inch x1 00

ai-inch x77 , x2 3 2

Fi eld 40 '

Fi eld 2 5 ' S.J .

Hynes

181 1 80 WS 41 5

Cat NGC 6981 M72

RA

Dec 20 52 . 1 -1 2 38 - - - - - - - - -

m 9 . 35

AD

5.1

Con Cl IX

Con

A ql' - - - - - - , ( 1 6t) Easily re solved on the outer edge s x70 ,. x 1 60 and x2 22 an area of resolved s tars on the NE s . � d e Se eill almo st separated by a dark region .

( 8 ) Even bri ghtness and di ffi cult to resolve wi th moderate aperture owing to i t s faintne s s . 416

NGC 7006

a

---­

1 0 . 67 2.2 I Del The bri ghtest stars in thi s clust er are 1 6 . 0 mag . Thi s is possibly an intergalac tic object l i ke NGC 241 9 . 2 1 00 . 3

+ 1 6 06

-

-

-

-

-

- -

.

( 1 6�) x84 bri ght centre surrounded by a nebulo us she l l . , x1 76 irregularly round wi th inner and outer parts showing i ll-defined edge s ; not re solved . ( 8�) x2 22 momentary glimp s e s of mottling at the c entre ; ( 6 ) Small wi th di ffuse nucl eus ; very i ll-defined . 41 7

NGC 7078 M1 5

2 1 28 . 8

NGC 7 006 8-inch x65

NGC 6 98 1 - M72 8-inch x1 00

Fi eld 42 '

Fi eld 40'

Glyn Jones

P . Brennan

+ 1 2 04

IV Peg Contains the 1 3 . 8 mag plane tary nebula Ps 1 , situated about 30 " NW of centre . Diam . of the nebula 1 " . - - - - - - - - - - - - - - - - - - - - - - ( 40 ) Very impre s sive ; re solved almo s t to the centre .

-

( 1 6�) Extremely bri ght core x7 0 ; x 3 3 3 c ompletel y fi l l s the fi eld ; easi ly resolvable . ( 8 ) Large area o f resolvable s tars around cen tre ; to tal s i z e not l e s s than 8 ' .

-------

41 8

NGC 7089 M2

Aqr 21 32 . 2 -00 56 1 1 .7 II The bri ghtest s tars in thi s clus ter are 1 3 . 2 mag.-

( 8� ) About 5 ' diam. , uniformly bri ght nucleus wi th s everal faint stars resolved on the edge s . es ( 8 ) Take s MP wel l ; outer edge s resolved and a t t i m

a greeni sh-blue glow surrounds the clus ter . ( 6 ) Very condensed ; outer areas re solved x1 20 .

NGC 7 078 - M1 5

NGe 7089 - M2

8-inch x1 00

8-inch x 1 00

Fi eld 40 '

Fi eld 40 ' K.

Glyn J ones

1 83

182 WS 41 9

Cat NGC 7 099 M30

RA

Dec -2 3 1 8

AD 8.9

Con Cl Co n V C ap - - - - ( 8�) x56 granul ar but not resolv ed ; x1 1 1 par ti al ly r e solved including a line of s tars extend ing N f�om the centre ; x22 2 extensive res oluti on , but no t i n any way t otal . ( 8 ) Bright nuc l eus about l ' - 2 ' diame ter surrounde d by a glowing area out to 5 ' ; the c entre i s den s e bu t 21 38.9

-

-

-

-

resolution o f the outer parts i s eas y . ( 6 ) Nebulous glow wi th bri ght , non-stel lar nucl eus . ( 3 ) Faint , elusive ; extends evenly from the centre .

NGe 7099 - M30 8-in ch x1 00 Fi eld 40'

Glyn J ones

1 85 A Catalogue o f Globular Clusters .

Descripti ons of a Further 1 0 Globular Clusters .

1 87

1 86 WS 420

4 21

Cat NGC 288

NGC 5 1 3 9 W Cen

RA

AD Dec m Con Cl Con 8 . 56 00 5 1 . 4 -26 44 1 2 .4 X Sol - - - - - - - - - - - - - - - - - - - - ( 40 ) 1 0 ' di am . ; beautiful object clearly reso l ve d

. ----

3 .65 65.4 1 3 2 5 . 3 -47 1 1 VIII Cen - - - - - - - - - - - - - - - - - - - - ( 40) Entire field covere d wi th go lden-red star s and succes sive fi elds show no thinning of the stars fo r a goo d number of move s in RA ; about 3000 star s se en . ( 1 6�) An unbeli evable s i ght ; x84 res olved to the centre ; no central core s e en , jus t countles s stars ; x1 7 6 more than fi lls the fi eld , and a number of d ark areas are vi sible whi le numerous small groups of s tars appear to curve acro s s the clus ter; behind all thi s is a diffuse nebul o s i ty due to the effect of thous.ands of unresolved stars .

422

NGC 5694

1 4 38 . 2

-26 2 5

10.17

2 .2

VII

Hya

( 1 0 ) x59 small and fai rly bri ght , more so towards the centre whi ch i s very compac t ; x1 48 the edge s appear to be on the verge of resolution and at x445 the cluster res olve s well . 42 3

NGC 6 2 9 3

Oph - - - -( 1 0 ) x59 a very compact core and a halo of parti ally res olved s tars ; resolved x44 5 , and appears sli ght ly extended E-W; bri ghter st ar near the E edge . 1 7 08 . 7

-26 32

IV

8 .79

------

424

NGC 6 304

1 7 1 3.0

-2 9 2 6

8 . 38

3.8

VI

Oph

- - - - - - - -

( 8 ) Compact and spheri cal ; re solution at x241 . -----Oph 1 7 1 5 . 0 -28 07 9 . 00 III 425 NGC 6 3 1 6 - - -

( 1 0 ) x59 pret ty bright , a little more s o towar d s the centre ; x2 9 6 re solution and some scattering seen .

Cat NGC 6 3 5 5 ,--

�1

Con Con C l AD Dec Oph 0 . 1 1 1 2 2 . 5 -2 6 1 9 - - - - - - - - - - - - ( 1 0 ) Qui te compac t ; s l i ght resolu tion a t x2 96 . RA

NGC 6366

Oph XI 5.8 1 0 . 09 -05 03 - - - ( 8 ) x1 4 5 beautifu lly resolved througho ut although a haze of unre s o lved s tars s til l evident .

NGC 6440

1 7 47 . 4

17 26.4

-20 2 1

V

Sgr

( 1 6�) Smal l , wi th bri ght core surround ed by a halo of nebulos ity; no resoluti on to x22 2 . ( 1 0 ) Compact obj ec t ; s l i ght re solution at x2 96 . NGC 6642

Sgr 0.8 8.8 1 8 2 9 . 9 -23 2 9 - - - - - - - - - - - - - - - - - - - - - - - ( 1 6�) Small , qui te bri ght wi th a small central core ; at x 1 7 6 very mottled at the edges wi th a few s tars re s olved , especial ly on the S edge ; more resoluti on on the edge s x 3 5 1 , the c entre remainin g bri ght .

1 89 LI ST O F ADDITIONAL OBJECT S . m AD Con Cl Dec RA Con 1 8 08 . 6 - 3 1 47 Sgr Thi s clu s t er i s obs cured by almo s t 2 . 5 magni tude s . 1 27 6

1 8 09 . 4

-07 1 4

6.0

XII

Ser

NGO 67 1 7

1 8 53 . 6

- 2 2 49

2.6

VI II

Sgr

NGO 6749

1 1 .7 1 9 03 . 9 + 0 1 44 Aq.1 Thi s clus ter i s obscured by almo s t 7 magni tud es .

10

The following three c lus ters are members of the Fornax dwarf galaxy (E3 ( d ) ) , a member of the Local Group of gal axi e s . There are two o ther globular c lu sters as s o ciated wi th thi s gal axy , but the s e are much fainter obj ec t s . NGC 1 049

Anon Anon

02 38 . 8 -34 4 1 1 1 .0 0.6 V For The bri gh t e s t clu s t er in the Fornax. sys t em , thi s obj e c t c an ac t as a locus for identification o f the remaining two clus t ers , who s e posi tions relative to NGC 1 049 are shown below. P o s it ioned 3 5 ' i n P A 203 0 from NGC 1 049 . P o s it ioned 1 7 ' in PA 1 6 5 0 from the first Anon c luster. An 8 mag s t ar l i e s about 7 ' p .

_APP ENDIX 1 .

1 91

CLASS 7 OPEN CLU STER S . General Catal o gue ( Sul ent i c and Tifft , 1 97 3 ) s 7 obj e c t s are defined as tho s e who s e image s are not aEparent the P al omar Sky Survey print s . There are many true ob j e c t s on th e se prints whi ch are rendered virtually invi sible due to heavy tamination by fi eld s t ars or extensive and intens'e regi ons o f s sion nebul o si ty . We have examined numerous open clus ters on Sky Survey prin t s , and many are very heavi ly swamped by fi el d s on both the E and O-print s . A c oup l e o f examp l e s are NGC 6800 NGC 6 8 1 5 , the l atter being l o c ated in an extremely rich fi e l d , no t appearing c lu s t er-l ike at all . Di s tributed over the sky are to be found many as teri sms o f s t ar s ; al l intents and purp o s e s they appear like rather spars e open ters , and a number have even found their way into Norton ' s S t ar as . Some of the s e are described in the fo l lowing pages , whi l e s are : NGC 2 3 1 8 , NGC 2 3 94 , NGC 241 3 and NGC 2 4 3 0 . O thers , not ted in Norton ' s are : NGC 1 524 , NGC 683 9 , NGC 6 8 56 , NGC 6 904 . Vi sual observers are abl e to i so l at e the s e asteri sms wi th eas e , the faint s t ars surrounding them in such l arge numbers are well the l i ght-gathering abi l i t i e s of moderate t e l e s cope s . In fol lowing page s are to be found obs ervati ons of 24 asteri sms ; the se are no t true clusters , the only avai l able data for them their p o s i t i ons , whi ch are shown for 1 97 5 . 0 . The obs ervations been made by Guy Hurs t ( 1 0-inch ) and P atri ck Brennan ( 6-inch ) .

1 92

193 Appendi x 1 .

Clus ter NGC 3 5 8

RA 01 03 . 6

Dec +61 54

Appendix 1 . C on C as -

-

2 3 56

( 1 0 ) In the same LP fi eld as NGC 366 ; 4 stars i n a sparse fi eld; c ould be no thing but an as teri sm . NGC 2026

05 4 1 . 7

+20 06

-

-

-

( 6 ) About 1 0 ' x 7 ' in si z e , showing a N-S elongati on ' , 3 5 s t ars from 9 mag down ; fainter s tars in clumps . NGC 2 1 6 5

06 09 . 0

+ 5 1 41

NGC 2 1 84;

06 09 . 7

-03 30

1 8 1 9 . 1 -1 6 48 Plotted in Norton ' s star Atlas .

Aur

( 6 ) Coarse , but bri ght ; an irregularly-shaped group about 6 ' di ameter; 1 5 stars of 1 0 mag and below.

of

06 28 . 0 + 1 6 42 Plotted in Norton ' s star Atlas .

6832

Cyg 1 9 47 . 7 + 5 9 2 1 - - - - - ( 1 0 ) Not ri ch , and very l ike an asteri sm ; c entred on a yellow 7 mag star wi th some evidence of faint er s t ars nearby ; s cattered s t ars of 8 to 1 2 mag.

6840

Aql + 1 2 02 - - - - - - - - - - - - - - - - - - ( 6 ) About 5 ' diameter , containing 2 0 s tars of 1 0 mag and below; a simi l ar but slightly poorer group , NGC 6843 , l i e s iO to the E .

6874

Cyg 20 06 . 9 + 3 8 1 0 - - - - - - - - - - - - - - - - ( 1 0 ) Rich group wi th considerabl e haz e ; shows a triangul ar- shaped outline and a 1 0 mag star on the E edge di splays an orange tint ; 1 9 s t ars in 7 ' area.

6896

Cyg 2 0 1 7 . 1 + 30 33 - - - - - - - - - - - - - - - - - - - - - - - ( 1 0 ) Two sligh t condensa tions of s tar group s in a rich fi eld; both s eem very like as t eri sms .

6989

Cyg 2 0 53 . 2 +45 1 1 - - - - - - - - - - - - - ( 1 0 ) Qui te l arge and faint ; two f aint doubl e s near the centre ; 1 0 ' di ameter ; 1 7 stars .

Ori

Gem

( 6 ) I rregular shap e ; contains about 40 s tars of 1 1 mag and below , unevenly di s tribute d ; 2 5 ' diameter. NGC 2260

06 3 6 . 8 -01 2 7 Plotted in Norton ' s star Atlas .

Mon

06 5 3 . 4

Mon

- - - - - - - ( 6 ) About 50 st ar s of 8 mag and below s cattered over a 2 0 ' area; roundi sh in shape .

NGC 2 306

-07 1 9

( 1 0 ) Large tri angle of tnree 8 mag s tars enclosin g fainter one s ; a 1 2 mag double l i e s at the centre and a very c lose 1 0 mag double on the S edge ; doubtful i f i t i s a true c luster ; 20' di ameter ; 2 7 stars .

Sgr

( 6 ) Rather poor ; contains s tars of 9 to 1 1 mag, and include s a triple of mags 9 : 9 : 1 2 .

( 6 ) Contains 3 5 stars of 9 mag and below di s tributed evenly acr o s s a 1 5 ' fi eld. NGC 2234

Con Gem

( 1 0 ) At LP shows as a nebulous 7 mag star , and at HP three 1 1 mag s tars form a tri angl e c l o s e to the 7 mag; fainter stars po s sible wi thin the 1 1 mag one s .

--­

T au

Dec + 1 4 01

RA 07 1 5 . 8

a

1 9 54 . 1

-

1 94

1 95 App endi x 1 .

Appendi x 1 . Cluster NGC 6997

RA 20 5 5 . 2

])ec +44 3 3

Con -

7) 52

C Ye; -

( 1 0 ) Fairly l arge but faint ; qui te ri ch in cer t ain areas wi th much haze ; contains several faint d o ubl eS j 1 2 ' di ameter ; 2 8 s t ars . NGC 7024

2 1 05 . 1

-

+41 24

-

2 1 09 . 7

+33 37

-

Cyg -

-

-

21 14.3

Cyg

+ 3 6 05

( 1 0 ) A very poor group containing two small as teri sm s j s t ar s scattered and faint . NGC 707 1

21 25.6

+ 47 49

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Cyg

-

-

-

( 1 0 ) Very smal l and di ffi cul t ; x1 20 a smal l , mi sty patch of s t ars from 1 2 mag downwards ; 4 ' di ameter. NGC 7 1 7 5

2 1 57 . 9

+ 54 42

-

-

Cyg -

-

( 1 0 ) Tri angular - shaped group wi th no bri ght stars ; rather sparse ; 8 ' di ameter ; 1 1 s t ars . NGC 7 2 3 4

22 1 1 . 2

+56 5 1

-

Ce p -

-

( 1 0 ) Extremely faint , showing as a 1 3 mag doub le s et in nebul o s i t y ; no t seen at LP ; 40 " di ameter.

-

-----Lac 2 2 2 7 . 4 + 5 2 42

NGC 7 2 9 5

-

( 1 0 ) Smal l , faint ; a 1 0 mag s t ar wi th o thers of 1 1 to 1 2 mag; about l ' di ameter .

-

2 2 49 . 5

-

-

-

-

-

+5 2 02' -

-

-

-

-

-

-

-

-

Lac

-

( 1 0 ) Between two 7 mag s t ar s ; faint and rather spars e ; 1 9 s t ars be tween 1 1 and 1 2 mag; 1 1 ' diameter. 7795

( 1 0 ) Rich but di ffi cul t as the maj ori ty of stars are below 1 2 mag; 7 ' di ameter; 1 0 s t ars . NGC 7 050

7 394

-

( 1 0 ) Ri ch c lus t ering of faint stars at the cen tre ; a smal l , faint c lus ter grouped around a 1 0 mag star ; 1 0 ' diameter; 1 4 s t ars . NGC 7037

( 1 0 ) Faint s t ars involved i n some haz e ; require s HP to pick out faint stars in a 5 ' are a.

Cy g -

Con C ep

])ec + 57 1 6

RA 2 2 38 . 7

23 57 . 4

-

-

-

-

+ 5 9 52

-

-

-

-

-

-

-

-

-

Cas

( 1 0 ) Faint , s c at t ered group ; a yellow 7 mag s t ar i s near the c entre , and the o ther s t ars are from 1 0 t o 1 2 magi 1 6 ' di ameter ; 17 s t ars .

1 97 APPENDIX 2 . FURTHER OBSERVATIONS OF OPEN CLUSTERS . The obs ervati ons depic ted on page s 1 98 and 1 9·9 were received af te r the main c atal o gue had been compi l e d . The obs ervatio ns were .ade by Guy Hurs t and Patri ck Brennan , and as wri tt en descriptio ns �er e not made for all of the c lus ters , we show below just posi tions {o r 1 97 5 , magni tude s and angular diameters exc ept for er 432 , for �hich no data i s avai lable barring RA and Dec . Guy Hurst : 1 0-inch spec . RA C luster 20 h 5 5� 6 NGC 6996 2 1 02 . 3 428 Cr 21 1 1 .3 432 Cr

+4 4 0

Dec 32 1

+44

29

+47

38

atri c k Brennan: 8 -inch spe c , 6-inch spec . C luster NGC 2489

RA 07 h 5 5 �2

NGC 6 6 3 1 NGC 7 7 6 2

18 23

25.8 48 . 6

_3 0 -1 2 +67

Dec 0 00 1 04 53

m 10. 1 8.5

�

AD 9.0 14.0

AD

9.2

8.5

11.5

4.0

10.0

1 1 .5

1 99

1 98

'.

NGC 6996 1 0-inch x80

Fi eld 1 5 '

G . Hur s t

COLLINDER 432 1 0-inch x1 20

G . Hurs t

P.

G . Hurs t

NGC 2489 6-inch x6 5 Fi eld 57 '

P . Brennan

8-inch x7 5

NGC 7 7 6 2 6-inch x6 5

Fi eld 44 '

Fi eld 57 '

NGC 6 6 3 1

COLLINDER 4 2 8 1 0-inch x1 20

Brennan

P . Brennan

20 1 APPENDIX 3 . THE DI STANCES OF CLUSTERS . In the chapters on the properti e s of open and glo bular c lus ter s d wel t bri efly upon c lus ter age s , and we now introduce the s e e again , the reason being that the age o f a clus ter , and i t s stance , are det ermined simultaneously . I n chapt€rs 2 and 5 we that stars spend mo s t of their lives on the main-sequence . The property of a main-sequence s t ar i s i ts mas s , the mo s t ive stars wei gh one hundred times as much a s the Sun , the least ive only a few times as much as Jupi te r. Once the mas s i s known , all o ther properties fol l o w , includi ng ameter , lumino s ity , surface temperature and life expectan cy. A ' s temperature i s measured by spectro s copy , thi s being the �.��.�vst parameter to obs erve , and thi s in turn determines the s t ar ' s no sity, provided we know that the s t ar i s a main-sequence obj e c t . the star ' s lumino s i ty and apparent magni tude we can deduce i t s tance , and the method of di stance determination known as spec tro­ pic parallax rel i e s on thi s principl e . There are subleties i n spec tral clas s i fic ation whi ch indi cate ther a s tar really is a main-sequence obj e c t , but they are no t to apply to faint clus ter s tars . EVen simple spe c tra are t ime­ g to obtai n , and a measure o f a s t ar ' s colour is adopted to charac teri s e properti e s . I f we measure the bri �htn e s s o f a t two wave lengths , in the blue ( B ) and vi sible ( V ) , we can taneously det ermine i t s colour and magni tude . A plot of V t B-V i s the colour-magni tude di agram , and the di fference en the di agram He have e xplained here and tho s e in Fi gure s 4 , and 7 i s that i n the l at ter three cases the V magni tude has been verted into the abso lute magni tude (M ) , whi ch i s the bri ghtn e s s obj ect would display a t a di stance ofv 1 0 pc . If we made up a colour-magni tude di agram for a given c luster wi th plo tted agains t B-V and then made up a diagram for a s econd c luster twi c e the di s t ance the colours of the s t ars would not change , but brightne s s would be reduc ed by about 1 . 5 mag. In a di agram for s s econd cluste r, therefore , the entire main-s e quence \{ould be fted 1 . 5 mag down the diagram , and we ",ould immediat ely recogni s e t the s econd c luster was more di stant than the firs t . Thi s i s not the end o f the s tory , however . \
2 02

203

Appendix 3 .

Wi th regard to gl obul ar clust ers , main- s e �uenc e fi tting invo l ve many correc tions to be as ac curate as could be wi shed ·' al so i t re �us . t o o . . �l:' e s · o b s ervat lons WhlCh are far from e asy to obtain . Bearing thi s in mln . t l· S advan t ageous that ano ther me thod of di stance determinatio n · s d • 1 � at hand , that of using RR Lyrae vari able s t ars . RR Lyrae vari able s are pres ent in varying numbers in many globul l:' c lus ters . They are to be found in the blue regions of the hori z on t a branches o f numerabl e c lu s ters , and obj e c t s such as Palomar 4 , wi th only a red s tub of a hori zontal branch , contain no RR Lyrae s t ars . The s e s t ars have periods of l e s s than one day , and are Popul ation 11 ob j e c t Wi th the absolute magni tud e s of RR Lyrae vari abl e s known , the di s tan S . moduli for the se s t ars in c lus t ers c an b e obtained and a di stan ce fi l:'e derived . Certain correc:tions may be appli ed , as for the effec t s of int ers tellar ab sorption and c ertain in� rinsic parame ters , but no gre at problem i s po sed by any o f the s e . Thi s me thod o f deriving the di st an c e s o f globular clus ters i s the mo s t reli abl e , and was used 50 years ago by Shapley and Sawyer .

�

�

No t all globular clusters contain RR Lyr�e variabl e s , however; metal­ rich clus ters wi th low z contain ei ther non.e or, at be s t , only a few relative to the hi gher l atitude me tal-poor clusters . In such cases an aid in obtaining di s t anc e s c an be to use the absorption in front of such obj e c t s .. For open clus ters the use o f classi c al Cepheid vari abl e s , Population I obj e c t s wi th periods be tween one and fi fty days , can be used to obtain di s t anc e s , but the number of known C epheids in open clus ters is not gre at . Many c lus ters have none at all , whi l e a very few clus ters harbO"J.r more than one . A further me thod for open c lusters utili s e s a correlation between the Trumpl er type of a clus ter and i t s intrinsic diameter . In thi s procedur e a ne arby clus ter of relatively well-determined di s tanc e and given type i s compared wi th a more di s t ant c luster of identical type . However , i t i s fel t that thi s i s not too re liable metho d . Error percentage s are , none thele s s , inherent in all di s t ance me asure s , 3-colour pho tomet ry o f clus ter s t ars , for exampl e , giving ri se to errors of the order of 2�/o . For thi s reason , consi derabl e effort i s expended in order to reduc e such errors as much as po s sibl e .

APPENDI X 4 . PHOTOGRAPHI C SOURCES FOR OPEN AND GLOBULAR CLU STERS . Below are listed a smal l number of sourc e s in whi ch pho tographs many c lusters of both typ e s can be found . Mo s t of the s e are e pr oduced in pro fe s si onal astronomic al j ournal s , whi ch are avai labl e in astronomi cal librari e s , such as that o f the Royal s tr onomi cal Soci e ty . The conc entration i s upon l e s s wel l-kn own bj ec t s , as many popular books on astronomy repro duc e pi cture s of he more common exampl e s . f

open Clus ters . M arkari an , B . E .

Grubussich, R .

1 96 9 , As tron . & As trophys . 2 , 22-27 . ( Ba 6 , NGC 2 2 54 ) .

Ki rat , A . Racine , R .

1 96 9 , Astr. J . 7 4 , 847 . ( Ro s 4 ) . 1 97 0 , Bull . Obs . Tonantzintl a y Tacubaya, 5 , 2 1 9-2 27 . ( NGC 2 1 7 4- 5 ) . 1 97 0 , As tron . & Astrophys � 9 , 2 2 1 -2 2 6 . ( NGC 2 2 36 ) .

Pi smi s , P . Rahim , M . Yi lmaz , F . Van den Bergh , S . Heeringa, R . Wagner , R . Sanders , W . L . Wo oden

11 ,

1 952 , A Pho tographi c A t las of Clusters and Nebulae . Mo scow. ( I nclude s the clusters NGC 366 , 6 3 7 , 6 6 3 , 1 502 , 2 3 62 , 640 5 , 6 47 5 , 649 4 , 68 2 3 , 687 1 , 6 9 1 3 , 7 1 60 , 7 5 1 0 , 7 7 88 ) . 1 96 5 , Z s . f . Ap . , 6 0 , 2 56 . (Markari an 5 0 ) .

W.H.

Turner , D . G . Herb s t" W . Laubert s , A.

1 97 0 , As tron . & As trophys . 8 , 2 1 3-222 . ( NGC 7 2 2 6 , 7 245 , IC 1 442 , Be 94 ) . 1 97 0 Astron . & Astrophys . 9 , 209-2 1 5 . (NGC 7 1 42 ) .

1 97 1 , As tron. & As trophy s . 1 4 , 2 8 3-292 . ( Ba 8 9 , Be 6 8 ) . 1 97 2 , As tron . & Astrophys . 1 9 , 1 5 5-1 58 . (NGC 68 1 9 ) . 1 97 4 , As tron . ( K 4 , Ba 1 0 ) .

&

Astrophys . 1 3 , 2 1 8-2 2 5 .

1 97 6 , PASP 88 , 308-3 1 1 . ( Lynds 8 1 0 ) . 1 97 6 , As tron . & As trophys . 5 2 , 3 0 91 3 1 1 . ( 3 new di s t ant clus ters ) .

204 Globul ar Clu s t ers . Alc aino , G . Ro sino , L . Pinto , G . T . Lloyd ' Evans , Menzi e s , J . W . Alc ainb , G .

He s ser � J . C .

205 APP ENDI X

Appendi x 4 .

1 97 1 , As tron. (NGC 48 3 3 ) .

&

5.

BI ELI O GRAP HY.

As trophys . 1 3 , 287-292 .

General . ]3 ecvar , A . 1 97 2 � in Variable stars in Globular Clu s t el:' and Related Sys t ems . Ed . J . D . Ferni e . Re i d e . GI yn J one s , K . (Palomar 2 , NGC 1 04 , 6 38 8 , 6 5 53 ) .

�

Al ter, G . 1 97 3 , Atlas o f Glo bular Clu s ters wi th Co l oul:'_ ]3aI az s , E . Magni tude Di agrams . Universidad Catolic a de uprecht , J . Chi l e . :Bas to s , A . (Numerous Clu s t ers i ncluding two P alomar obj e c t s ) . 1 97 6 , PASP 8 8 , 849-8 5 7 . open Clu s t ers . (NGC 6 3 0 4 , 6 3 5 2 , 644 1 ) . :Bec.ker , w.

1 96 0 , Atlas Coeli Katalog. 1 968 , Me s si er ' s Nebulae and Star Clu s t er s .

Prague . Faber .

1 97 0 , Catalogue o f S t ar Clus ters and As s o ciat ion s . 1 97 4 , C e l e s tial Obj ec,t s and Satelli t e Astronomy

Eudape s t . Europ . Spac e Re s . Org.

1 97 2 , in The Rol e o f Schmi dt Tel escopes in Astronomy . ( Ed . U . H aug )

SRC/ESO .

•

As trophys . 2 5 , 7 1 - 77 .

Burki , G . Maeder , A .

1 97 3 , As tron .

Fawley , W . M .

1 97 4 , Ap . J . 1 9 3 , 367- 3 7 2 .

Fi t zgeral d , :t-1 . P . Moffat , A. F . J .

1 97 4 , As tr . J . 7 9 , 8 7 3-884 .

Fi t zgeral d , M . P . Moffat , A . F. J .

1 97 4 , PASP 86 , 480-48 5 .

Garri son , R . F. Kormendy , J .

1 97 4 , J ourn . Roy . As t r. Soc . Canada, 68 , 263.

Sandule ak , N .

1 9 7 4 , PASP 86 , 7 4-7 5 .

Strom , S. E . & K . M . Carrasco , L .

1 97 4 , PASP 8 6 , 7 98-805 .

Grasdalen, G . L . Carrasc o , 1, .

1 97 5 , Astro n .

&

As trophy s . 43 , 2 59-2 6 5 .

HaS S all , S .M .

1 97 5 , Astro n .

&

As trophy s . Supp . 2 0 , 2 5 5-267 .

Samson, W . L .

1 97 5 , Astrophys . Sp . Sc L 3 4 , 3 7 7 - 38 6 .

Wallenqui s t , A .

1 97 5 , Nova Ac ta Regia e So c . Sci . Upsal i ens i s S er . V : A 2 , 1 -9 8 .

&

206

Appendi x 5 . &

Fi t z geral d , M . P . Mo ffat , A . F. J .

1 97 6 , Astron .

McClure , R . D . Twarog, B . A .

1 97 7 , Ap . J . 2 1 4 , 1 1 1 - 1 2 3 .

:r.1 offat" A. F. J . Fi tzgeral d , M .P . J ackson , P . D .

1 97 7 , Ap . J

0'

As trophys , 5 0 , 1 49- 1 52 .

2 1 5 , 1 06- 1 1 8 .

Globular Clus ters . Arp , H . C .

1 96 5 , in Galac tic struc ture . S tans & S te l l ar Sys t ems , Vo l . 5 . ( Ed . A . Blauuw & M . Schmi dt ) .

Ro sino , 1 . Pinto , G .

1 97 2 , in Vari abl e stars in Gl obular Clus ters & Related Sys tems . ( Ed . J . D . Ferni e ) .

Alc aino , G .

1 97 3 , Atl as of Globular Clus ters wi th Colour-f.ragni tude Di agrams .

Dickens , R . J .

1 97 4 , i n Re search Programmes for the New 1arge Telescope s . (Ed . A . Rei z ) .

Harri s , W .. Racine , ,R .

1 97 4 , Journal Roy . As tr . So c . Canada, 68 , 263 .

Kukarkin , B . V .

1 97 4 , The Globul ar Star Clus t ers .

Bahcall , N. A . Hausman " M . A .

1 97 6 , Ap ., J . 1e t t . 207 , 1 1 8 1 - 1 84 .

Gursky , H . Bahcall , J .N .

1 976 , Ap . J . 208 , 47- 5 1 .

Harri s , W . E . Hes ser , J . A .

1 97 6 , PASP 88 � 377-37 9 .

Wehl au , A . Hogg, H . S .

1 97 7 , Astr . J . 82 , 1 37 - 1 49 .

We,S t, R .M . Bartaya" R . A .

1 97 9 , ESO Sci . Preprint No . 4 1 .

Chi cago .

Reide l . Chi l e .

ESO/SRC/CERN .

Moscow .

Webb Society Deep-Sky Observer's

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