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Observational Data for Galactic Globular Clusters

	Brian A. Skiff
	Lowell Observatory
	1400 West Mars Hill Road
	Flagstaff  AZ  86001-4499
	Internet:  bas@lowell.edu
	
	
	Abstract
	     An up-to-date tabular summary of total magnitudes, brightest stars, and 
	journal references is given for all 142 confirmed Galactic globular clusters.
	The text discusses how the information can be used to plan and analyze visual
	observations.
	
	
	Introduction
	     What you can observe depends a lot on what you know about.  It is easy,
	for instance, to overlook a bright non-NGC galaxy in the same field as an
	NGC object merely because it is not plotted on the atlas you're using.  To
	help improve this situation, over the years I have collected relevant data 
	about all types of objects from the professional literature for use in 
	analyzing my visual observations.  Much of this material was condensed 
	without attribution into Chris Luginbuhl's and my 'Observing Handbook and 
	Catalogue of Deep-sky Objects'.  But a lot of data has come out since 1984, 
	when work for the book was finished.  Many of the most useful articles were 
	mentioned in the `Scanning the Literature' column that appeared in the back 
	pages of each issue of late, lamented 'Deep Sky' magazine.  I continue to
	get inquiries from amateurs about specific objects, and it is usually possible
	to supply a citation to a relevant journal article dealing with practically 
	any fairly bright object.  This task has become much easier in the last 
	several years thanks to the availability of on-line databases, such as the 
	NASA Extragalactic Database (NED) and SIMBAD, maintained by the Centre de 
	Donne\'es astronomiques in Strasbourg, France.
	     One file I've built up that has come in particularly handy is a list of
	`observables' for globular clusters.  The list of globulars is taken from the
	compilation by Djorgovski & Meylan (ref. 1), and lists all confirmed clusters
	deemed to belong to the Galaxy and classified as globulars.  Comments about
	objects omitted and undetermined cases are dicussed below.  Included in the 
	file are total V magnitudes according to the 1992 Peterson compilation (ref.
	2).  In addition, I went through the literature and found essentially every 
	photometric study ever published of a globular cluster (hundreds of papers!).
	From these publications, I determined the V magnitude and B-V colour of the 
	brightest stars in each cluster, and the magnitude of the `horizontal branch'.
	For each cluster I chose the best paper (sometimes more than one) dealing 
	with the brighter stars.  That is, I have listed in the bibliography the paper
	with the most useful finder chart for the field of each cluster, the one with
	magnitudes for bright field stars around the cluster---the best one for 
	checking one's visual and photographic observations.  This is not always the 
	highest-quality or most recent study, just the one best for amateur purposes.
	This material is collected in Table 1.
	
	Colour-Magnitude Diagrams
	     The purpose in making photometric measurements of globular cluster stars
	is to create a `colour-magnitude diagram'.  This is merely the observational
	version of the well-known Herzsprung-Russell diagram.  In the original HR
	diagram, the luminosity of a star (or group of stars) is plotted against the
	temperature.  We cannot observe these two things directly, but we can measure
	the apparent brightness of a star and its `colour', that is, the difference in
	its brightness at two wavelengths.  A hot star is brighter toward the blue 
	end of the spectrum than toward the red end, and conversely for cool stars.  
	In the commonly used UBV system, the temperature of a star can be estimated 
	by the magnitude difference in the B (blue) and in the V (visual) band.  The 
	B-V ("B minus V") colour for a fairly hot star like Vega is close to zero in 
	this system and is about 1.5 for ordinary cool giants such as Aldebaran.  
	Some cool supergiant stars and carbon stars have much larger B-Vs, and appear 
	quite red visually.  The hottest ordinary stars, such as the stars in the 
	Belt of Orion, have B-V about -0.2.  Interstellar dust causes stars to appear
	redder than they would than otherwise, and so more distant stars are often 
	`reddened' by significant amounts.
	     Well, what happens when B and V magnitudes are measured for stars in
	a globular cluster?  The figure shows an excellent example from a paper by
	Gonzalo Alcaino and William Liller (ref. 3).  Notice first that the stars do 
	not scatter everywhere in the plot of V versus B-V, but instead clump into 
	narrowly-defined strands, called `sequences' or `branches'.  The very 
	brightest stars in any globular cluster are stars at the tip of the red-giant
	branch toward the upper right corner of the plot.  These are giants and 
	bright-giants of spectral class K and M.  They have evolved from stars 
	somewhat more massive than the Sun.  Following the red-giant branch down, the
	more nearly vertical string of stars is called the subgiant branch, i.e., 
	stars intermediate in brightness between main-sequence stars (like the Sun) 
	and the brighter, cooler giants.  Midway down this string, stars split off to
	the left (blueward) side of the diagram.  These stars are called `horizontal-
	branch' stars, and are even more evolved than the red giants, i.e., stars that
	are heading toward extinction.  In the middle of the horizontal branch is a 
	band of variables, the RR Lyraes, indicated by small x's in this plot.  These
	are A- and F-type stars (somewhat hotter than the Sun) that pulsate with 
	amplitudes of around a magnitude with periods of about half a day.
	     At the base of the red-giant/subgiant strip, the stars take a sharp
	turn redward as they get fainter.  This is point where the most massive stars
	on the main-sequence are starting to evolve into giants.  The stars at the
	turnoff in globular clusters are close to the Sun's temperature and mass. 
	From here on down as far as anyone has been able to observe in any cluster, 
	there are only unevolved main-sequence stars, becoming more and more numerous
	toward the faint end.  The faintest stars measured in globulars so far are
	about absolute V magnitude 12, or eight magnitudes fainter than the Sun,
	corresponding to stars of only 0.2 of a solar mass.  The most luminous stars
	at the tip of the red-giant branch, on the other hand, have absolute V
	magnitudes near -2.5, roughly half a million times brighter.
	     Interpreting colour-magnitude diagrams for clusters in terms of a star's
	evolutionary history remains a central problem for astrophysics even 75 years
	after the first diagrams were constructed and their significance shown.  For
	further reading on this subject, see for instance refs. 4 & 5.  But these 
	details need not concern us for the immediate purpose visual observation.
	
	What Are The Data Good For?
	     In visual observation of a globular cluster, obviously if you are going
	to see any resolution at all, your telescope will have to show stars at least
	as faint as the brightest stars in the cluster.  Thus it is of interest to 
	know what the magnitudes of the stars in the cluster are in order to predict
	whether a cluster will be resolved, or perhaps to get an estimate of how faint
	you can see based on whether a cluster is resolved or not.  So the table
	includes the magnitudes and colours for the very brightest stars in the
	cluster [V(tip) and B-V(tip)].  I note the B-V colour because the eye will see
	red stars fainter than their V magnitudes would indicate, since the peak 
	dark-adapted visual response is shifted toward the blue from the standard V 
	passband.  The shift amounts to roughly:
	
	m(vis) = V + 0.2(B-V).  
	
	For example, a star with B-V = 1.5 will appear 0.3 magnitudes fainter 
	visually than a star of B-V = 0.0 that has an identical V magnitude.  As you
	can see by looking down the list, stars at the tip of the giant branch in
	most globulars have B-V between 1.5 and 2.0.  So although these stars will
	appear slightly fainter than blue stars of the same V magnitude, comparisons
	among different globulars can be made without taking this effect into account.
	     In moderate-to-large apertures, most globulars are at least partially
	resolved, showing some dozens of stars.  In the brightest objects, one often
	sees seemingly thousands of stars, and in a few such as 47 Tucanae and omega
	Centauri, it really is thousands.  The cluster is `well resolved'.  The point
	at which this happens is when your telescope has a limiting magnitude at or 
	below the level of the horizontal branch.  The reason is simply that the 
	number of stars in any given magnitude interval takes a sudden leap at the 
	magnitude of the horizontal branch.
	     What about the Shapley-Sawyer concentration classes?  These Roman numeral
	classes are often considered indicative of how easy a cluster is to resolve.
	The classes are actually correlated with central surface brightness, not the
	magnitudes of the stars, and my experience indicates they have little bearing
	on cluster resolution.  In general, the highly-concentrated clusters are the
	most distant ones, and so are difficult to resolve simply because the stars 
	are faint, not because they are close together.  I have seen the brightest 
	handful of stars in M15 and M2 using a 70mm refractor at 75x and 110x.  They 
	are both quite strongly concentrated objects, yet their brightest stars, 
	between mag. 12.5 and 13.0, are just visible in this small aperture from a 
	true-dark site.  It may be that clusters with the same V(tip) but having 
	different concentration classes will show a difference in resolution.  Perhaps
	a reader can provide the necessary observations.
	
	Cluster Rankings
	     Along with the main list, the supplementary lists (Tables 2,3,4) show how
	the clusters rank in terms of the three parameters:  total magnitude, 
	magnitude of the brightest stars, and by magnitude of the horizontal branch.
	The results are occasionally surprising compared to conventional wisdom.  The
	first list shows the twenty-five clusters with total V of 7.0 or brighter.  
	The two southern clusters omega Centauri and 47 Tucanae are roughly a 
	magnitude-and-a-half brighter than the nearest competition.  M5 and M13 rank 
	seventh and eighth; they are nice clusters, but by comparison omega Cen and 
	47 Tuc will knock your socks off!  A common debate among southern observers
	is which of the two is better.  Some prefer the sheer richness of omega Cen,
	and others the star-density and remarkable (indeed unique) structure of 47 
	Tuc.  Essentially all of the non-Messier clusters in the list are far-southern
	objects that certainly would have been catalogued by him had he worked at 
	southern latitudes.  NGC 3201 and NGC 6541 are accesible, however, to those 
	at mid-northern latitudes.
	     The other two lists give the top ten clusters in terms of brightest stars
	and brightest horizontal branches---the most easily resolved clusters.  Note 
	that neither omega Centauri nor 47 Tucanae appears at the top of these lists.
	Both are luminous objects with large numbers of stars, as anyone who has
	observed them can confirm, and their combined light sends them to the top of
	the total magnitude list.  But because of their distance, the brightest stars
	are not as bright as nearer clusters.  Instead the winner is NGC 6397, a 
	far-southern object that is known as the closest or second-closest globular 
	(it and Messier 4 are both about two kiloparsecs distant).  This object and 
	the next few in the ranking are partially resolved in ordinary handheld 
	binoculars.  For northern observers, the most easily resolved clusters are
	M22, M4, and M55, all of which are nevertheless south of -20 Dec.  The 
	brightest stars in M13 are nearly two magnitudes fainter than those in 
	NGC 6397.  On the horizontal-branch list, NGC 6397 also rates as #1, again 
	with stars two magnitudes brighter than those in M13, which falls off the list
	altogether.  
	     Perhaps the most immediate lesson to be drawn from this is that to see 
	the galactic globular system well at all, you need to head to the southern 
	hemisphere!
	
	The Database
	     The objects contained in Table 1 derive directly from Djorgovski & 
	Meylan's list (ref. 1), which was presented at a 1992 conference.  They 
	included 143 objects, but one of them, known as the "Reticulum cluster", has 
	since been shown to be an outlying member of the Large Magellanic Cloud.  The
	cluster reported by Djorgovski as "Djorgovski 3" is identical with NGC 6540, 
	which was previously considered to be an open cluster.  This is the first 
	NGC/IC object to be identified as a globular since the 1930s.
	     Since they are relatively easy to pick up visually in moderate apertures,
	I have also included the five globular clusters in the Fornax system.  The
	Clouds appear to contain only another eight or ten true globulars, and along
	with the "Fornax five", appear to be the only globulars outside the three 
	major spirals in the Local Group (M31, M33, and Milky Way).  Yes, I know
	Uranometria and the RNGC indicate scores of globulars in the LMC, but those
	clusters are not similar to galactic globulars.  (Let's talk about this
	another time.)
	     According to preliminary studies, Palomar 1 exhibits no horizontal-
	branch stars, and thus is likely to be an old open cluster.  I've left it in 
	the list for now since the work is not formally published.
	     It is also worth noting that E 3, AM-2, and AM-4 are evidently clusters of
	intermediate age, i.e. between the ages of the oldest ordinary open clusters
	(6-8 billion years) and those of globulars (13-15 billion years).  Although
	not uncommon in the Magellanic Clouds, these appear to be essentially absent
	from the Milky Way.  One can suspect that, over the course of the dynamical
	evolution of the Local Group of galaxies, the Milky Way has glommed onto a 
	couple of stray clusters from other galaxies.  Indeed this may help explain 
	the bi-modal character of the Galactic globular cluster system.
	     If you are one of those cluster-fetishists familiar with obscure objects
	on older lists of globulars, you will notice a number of objects missing and 
	others that are new.  Most of the nebulous objects reported as possible 
	globulars by A. Terzan and his collaborators turn out to be galaxies or 
	planetary nebulae upon spectroscopic investigation.  Still, for several of 
	these no definitive conclusion has yet been reached.  Djorgovski & Meylan 
	indicate that the objects TJ 5, TJ 23, and TBJ 3 could be either distant, 
	obscured globulars, chance groupings of stars, or background galaxies with 
	Milky Way stars superposed.  Other "suspect" objects are:
	
	ESO 166-SC11 = UKS 2, probably an open cluster;
	ESO  93-SC?08, probably an open cluster;
	ESO 224-SC08 = vdB-H 176, a sparse globular or an open cluster.
	
	More data are required for all these six objects.  
	     Among objects confirmed to be "not globular" are the Terzan objects 
	TBJ 1 = TJ 17, TBJ 2 = TJ 16, TJ 15, and others, all of which are galaxies.
	Grindlay 1 and Kodaira 1 are both nonexistent, there being no cluster at the 
	published coordinates of either.
	
	
	     I maintain this list on a computer and keep it up to date as new journal
	articles are published.  Contact me if you would like a copy of the latest 
	version.  Ordinary mail and electronic mail are the best ways to get my 
	attention.  If you have an e-mail connection (or know someone who does), it 
	is easy for me to simply send you the current file.
	
	
	References
	1.  Djorgovski, S. G., and Meylan, G.  1993, "The Galactic Globular Cluster
	     System:  A List of the Known Globular Clusters and Their Positions"; in
	     'Structure and Dynamics of Globular Clusters', A.S.P. Conference 
	     Series vol. 50, S. G. Djorgovski and G. Meylan, eds., pg. 325.
	     
	2.  Peterson C. J.  1993, "Integrated Photometric Properties of Globular
	     Clusters"; in 'Structure and Dynamics of Globular Clusters', A.S.P. 
	     Conference Series vol. 50, S. G. Djorgovski and G. Meylan, eds., pg. 337.
	
	3.  Alcaino, G., and Liller, W.  1984, "BVRI Main-Sequence Photometry of the
	     Globular Cluster M4", 'Astrophys. J. Suppl.', 56, 13.
	
	4.  Bok B. J., and Bok, P. F.  'The Milky Way', Harvard Univeristy Press,
	     Cambridge MA, 1981.
	
	5.  Payne-Gaposchkin, C.  'Stars and Clusters', Harvard University Press,
	     Cambridge MA, 1979.
	
	
	
	
	
	
	Table 2.  Globular clusters brighter than V = 7.0
	
	Name               V
	N5139=omega Cen   3.9   
	N 104=47 Tuc      4.0   
	N6656=M22         5.2   
	N6397             5.3   
	N6752             5.3   
	N6121=M4          5.4   
	N5904=M5          5.7   
	N6205=M13         5.8   
	N6218=M12         6.1   
	N2808             6.2   
	N6809=M55         6.3   
	N6541             6.3   
	N5272=M3          6.3   
	N7078=M15         6.3   
	N6266=M62         6.4   
	N6341=M92         6.5   
	N6254=M10         6.6   
	N7089=M2          6.6   
	N 362             6.8   
	N6723             6.8   
	N6388             6.8   
	N6273=M19         6.8   
	N7099=M30         6.9   
	N3201             6.9   
	N6626=M28         6.9   
	
	
	Table 3.  Ranking by brightest stars
	
	Name                V
	N6397             10.0 
	N6752             10.5 
	N6656=M22         10.7 
	N6121=M4          10.8 
	N6809=M55         11.2 
	N5139=omega Cen   11.5 
	N3201             11.7 
	N 104=47 Tuc      11.7 
	N6205=M13         11.9 
	N6254=M10         12.0 
	
	
	Table 4.  Ranking by horizontal-branch magnitude
	
	Name                V
	N6397             12.9   
	N6121=M4          13.4   
	N6752             13.8   
	N 104=47 Tuc      14.1   
	N6656=M22         14.2   
	N6809=M55         14.4   
	N6838=M71         14.4   
	N5139=omega Cen   14.5   
	N6254=M10         14.7   
	N3201             14.8   
	
	Globular Cluster Diameters, Integrated Magnitudes, Brightest Stars, and 
	Horizontal Branch Levels
	version:  2 May 1999
	
	notes:  ESO 452-SC11, IC 1257 added, AM-2 deleted (is old oc), Terzan 10 added
	
	
	Name                  RA  (2000)  Dec     Diam(')    Vt   V(tip)  B-V(tip)  V(HB)  
	                                        mu22 mu25
	NGC 104 = 47 Tuc     0 24 05  -72 04.9    24   50    4.0   11.7     1.7     14.1   
	NGC 288              0 52 48  -26 35.4   5.5   13    8.1:  12.6     1.8     15.3   
	NGC 362              1 03 14  -70 50.9   6.1   14    6.8   12.7     1.7     15.4   
	Fornax-1             2 37 02  -34 11.0        0.9   15.6   18.3     1.3     21.3   
	Fornax-2             2 38 44  -34 48.6              13.5   19.0     1.3     21.3   
	NGC 1049 = Fornax-3  2 39 48  -34 15.4              12.6   18.4     1.2     21.3   
	Fornax-4             2 40 07  -34 32.3              13.6   18.6     1.2     21.3   
	Fornax-5             2 42 21  -34 06.2        1.7   13.4   18.6     1.3     21.3   
	NGC 1261             3 12 15  -55 13.0   3.2  6.8    8.3   13.5     1.7     16.8   
	Palomar 1            3 33 23  +79 34.8        2.8   13.6:  16.3     1.2:           
	AM-1 = E 1           3 55 03  -49 36.9        0.5   15.8:  18.2     1.5     20.9   
	Eridanus             4 24 45  -21 11.2              14.7:  17.6     1.5     20.4   
	Palomar 2            4 46 06  +31 22.9        2.2   13.0:  18.8:            21.7
	NGC 1851             5 14 06  -40 02.8   4.5   12    7.1   13.2     1.7     16.1   
	NGC 1904 = M79       5 24 11  -24 31.5   3.8  9.6    7.7   13.1     1.6     16.2   
	NGC 2298             6 48 59  -36 00.3   2.2    5:   9.3   13.4     1.3     16.2   
	NGC 2419             7 38 08  +38 52.9   1.6  4.6   10.3   17.3     1.4     20.2   
	Pyxis                9 07 57  -37 13.6          2:         15.2     2.8     18.7
	NGC 2808             9 12 03  -64 51.8   6.5   14    6.2   13.8     1.9     16.1   
	E 3                  9 20 59  -77 17.0              11.4:  17.0:    1.1:     --    
	Palomar 3           10 05 31   +0 04.3        1.6   13.9:  18.0     1.2     20.5   
	NGC 3201            10 17 37  -46 24.7   7.8   20    6.9   11.7     1.7     14.8   
	Palomar 4           11 29 17  +28 58.4        1.3   14.2:  18.0     1.4     20.8   
	NGC 4147            12 10 06  +18 32.5   1.6  4.4   10.4   14.5     1.2     16.9   
	NGC 4372            12 25 45  -72 39.4          5:   7.2   12.2     2.0     15.6   
	Ruprecht 106        12 38 40  -51 09.0          2:  10.9:  14.8     1.6     17.8   
	NGC 4590 = M68      12 39 28  -26 44.6   4.3   11    7.3   12.6     1.3     15.6   
	NGC 4833            12 59 35  -70 52.5               8.4   12.4     1.7     15.5   
	NGC 5024 = M53      13 12 55  +18 10.2   5.1   13    7.7   13.8     1.6     16.9   
	NGC 5053            13 16 27  +17 41.9         10    9.0   13.8     1.5     16.9
	NGC 5139=omega Cen  13 26 46  -47 28.6    29   55    3.9   11.5     1.7     14.5   
	NGC 5272 = M3       13 42 11  +28 22.7   7.4   18    6.3   12.7     1.7     15.7   
	NGC 5286            13 46 27  -51 22.4   5.1   11    7.4   13.5     1.8     16.5   
	AM-4                13 56 21  -27 09.7              15.9   20.5:    0.5     21.6   
	NGC 5466            14 05 27  +28 32.1   3.0  9.0    9.2   13.8     1.3     16.6   
	NGC 5634            14 29 37   -5 58.6   1.8  5.5    9.5                    17.8
	NGC 5694            14 39 37  -26 32.3   1.6  4.3   10.2   15.5:    1.3:    18.5:  
	IC 4499             15 00 19  -82 12.8   2.2  8.0   10.1   14.6     1.6     17.7   
	NGC 5824            15 03 59  -33 04.1   2.5  7.4    9.1   15.5     1.6     18.5   
	Palomar 5           15 16 05   -0 06.7        3.2   11.8:  15.5     1.1     17.4   
	NGC 5897            15 17 25  -21 00.6   4.5   11    8.4   13.3     1.8     16.3   
	NGC 5904 = M5       15 18 34   +2 05.0    11   23    5.7   12.2     1.6     15.1   
	NGC 5927            15 28 01  -50 40.4   4.6    6:   8.0   14.5     2.2     16.6   
	NGC 5946            15 35 29  -50 39.6          3:   8.4                    17.2
	NGC 5986            15 46 04  -37 47.2        9.6    7.6   13.2     1.7     16.5   
	Palomar 14          16 11 00  +14 57.8              14.7:  17.6     1.3     20.0   
	NGC 6093 = M80      16 17 03  -22 58.5   4.5   10    7.3   12.5     1.8     15.6   
	NGC 6121 = M4       16 23 36  -26 31.5    15   36    5.4   10.8     1.8     13.4   
	NGC 6101            16 25 49  -72 12.1   3.0    5:   9.2   13.5     1.8     16.6   
	NGC 6144            16 27 14  -26 01.5   3.7   17    9.0   13.4:    1.7:    16.5:  
	NGC 6139            16 27 40  -38 50.9   2.7  8.2    9.1   15.0     1.5:    17.9
	Terzan 3            16 28 41  -35 20.6              12.0:  15.0     2.2     17.3
	NGC 6171 = M107     16 32 32  -13 03.2   4.2   13    7.8   13.0     1.9     15.6   
	ESO 452-SC11        16 39 25  -28 23.9                     15.3:            16.6
	NGC 6205 = M13      16 41 41  +36 27.6    10   20    5.8   11.9     1.6     15.0   
	NGC 6229            16 46 59  +47 31.7   2.0  4.5    9.4   15.5     1.5     18.0   
	NGC 6218 = M12      16 47 15   -1 56.9   7.4   16    6.1   12.0     1.7     14.6   
	NGC 6235            16 53 25  -22 10.6   2.2    5:   8.9   14.0:    1.8     16.7   
	NGC 6254 = M10      16 57 09   -4 06.0   8.5   20    6.6   12.0     1.6     14.7   
	NGC 6256            16 59 33  -37 07.3   1.2  4.1   11.3:  15.3:    2.7:    18.2:  
	Palomar 15          16 59 51   -0 32.5              14.2   17.1     1.8     19.9   
	NGC 6266 = M62      17 01 13  -30 06.8   7.2   15    6.4   13.2:    2.0:    16.3:
	NGC 6273 = M19      17 02 38  -26 16.1   7.0   17    6.8   14.0?    1.8:    17.0   
	NGC 6284            17 04 29  -24 45.9   3.1         8.9                    16.6
	NGC 6287            17 05 09  -22 42.5   2.4         9.3   14.5:    1.8:    17.1:
	NGC 6293            17 10 10  -26 34.9   4.1         8.3   14.3     1.4     16.5:  
	NGC 6304            17 14 32  -29 27.7   4.3    8:   8.3   14.2:    2.1:    16.2   
	NGC 6316            17 16 37  -28 08.4   2.7         8.1   16.0:            17.8   
	NGC 6341 = M92      17 17 07  +43 08.2   7.0   14    6.5   12.1     1.3     15.1   
	NGC 6325            17 17 59  -23 46.0   1.6  4.1   10.2   14.7?    2.4:    17.3:  
	NGC 6333 = M9       17 19 12  -18 31.0   4.5   12    7.8   13.5     1.7     16.2:  
	NGC 6342            17 21 10  -19 35.2   2.2         9.5   15.0:            16.9   
	NGC 6356            17 23 35  -17 48.8   3.9   10    8.2   15.1     2.2     17.7   
	NGC 6355            17 23 59  -26 21.2   2.1         8.6                    17.2
	NGC 6352            17 25 29  -48 25.4          9:   7.8   13.4:    1.7     15.1   
	IC 1257             17 27 08   -7 05.6          5:  13.1   17.5:    1.8:    19.8
	Terzan 2            17 27 33  -30 48.2        0.6   14.3:                   19.8:
	NGC 6366            17 27 44   -5 04.6   3.6   13    9.5:  13.6     2.2     15.7   
	Terzan 4            17 30 39  -31 35.7              16.0:                   21.6?
	Haute-Provence 1    17 31 05  -29 58.9   0.4: 1.2   12.5:  16.0             18.6
	NGC 6362            17 31 55  -67 02.9   5.6   15:   8.1   12.5     1.7     15.5   
	Liller 1            17 33 25  -33 23.4              15.8:  20.5:            24.4:
	NGC 6380 = Ton 1    17 34 28  -39 04.2   1.8        11.5:  17.0             19.5
	Terzan 1            17 35 47  -30 28.9              15.9:                   20.6:
	Ton 2 = Pis 26      17 36 11  -38 33.2              12.2                    18.2
	NGC 6388            17 36 17  -44 44.1   5.2         6.8   14.8     2.1     17.2   
	NGC 6402 = M14      17 37 36   -3 14.8   5.5   11    7.6   14.0     2.3     17.2   
	NGC 6401            17 38 37  -23 54.6   2.4         7.4                    17.3
	NGC 6397            17 40 41  -53 40.4    12   31    5.3   10.0     1.5     12.9   
	Palomar 6           17 43 42  -26 13.4   0.6        11.6:                   19.1   
	NGC 6426            17 44 54   +3 10.2   1.0  4.2   10.9   15.2     1.8     18.1
	Djorgovski 1        17 47 28  -33 03.9              13.6:  
	Terzan 5            17 48 05  -24 46.8   0.4  2.4   13.9:  20.5:            22.5:
	NGC 6440            17 48 53  -20 21.6   2.2         9.3   16.7:    2.3:    18.7  
	NGC 6441            17 50 13  -37 03.1   4.8         7.2   15.4:    2.3:    17.1   
	Terzan 6            17 50 46  -31 16.5   0.2  1.4   13.9:  20.5:    2.5:    22.3:
	NGC 6453            17 50 52  -34 36.0   3.8        10.2                    17.7
	UKS 1               17 54 27  -24 08.7              17.3:  22?              25.5
	NGC 6496            17 59 03  -44 16.0   2.8         8.6   14.3     1.8     16.5   
	Terzan 9            18 01 39  -26 50.4        0.2   16.0:                   20.3:
	ESO 456-SC38        18 01 49  -27 49.6        9.9:         15.5:            17.5:
	NGC 6517            18 01 51   -8 57.5   1.5  4.0   10.1   16.0?    2.2:    18.0:  
	Terzan 10           18 02 57  -26 04.0                     19.7:            22:
	NGC 6522            18 03 35  -30 02.1   4.7         9.9   14.1:    2.1     16.9   
	NGC 6535            18 03 51   -0 17.8   0.8  3.4    9.3   12.8     1.9     15.7   
	NGC 6528            18 04 50  -30 03.4   2.5         9.6   15.5:    2.0:    17.1   
	NGC 6539            18 04 50   -7 35.2   2.1  7.9    8.9   15.9             18.3:  
	NGC 6540            18 06 09  -27 45.9
	NGC 6544            18 07 21  -24 59.9   4.6         7.5:  12.8:    2.1:    15.0:  
	NGC 6541            18 08 02  -43 42.9         15    6.3   12.1     1.8     15.2   
	NGC 6553            18 09 16  -25 54.5   4.6         8.3   15.3     2.4     16.9
	NGC 6558            18 10 18  -31 45.8               8.6                    16.7
	IC 1276 = Pal 7     18 10 45   -7 12.8   1.3  8.0   10.3:  15.7     2.4     17.7
	Terzan 11           18 12 15  -22 44.5              16.4:  18.5?            20.5:
	NGC 6569            18 13 39  -31 49.6   3.2         8.4                    17.1
	NGC 6584            18 18 38  -52 12.9   3.3:        7.9   13.5     1.7     16.5   
	NGC 6624            18 23 41  -30 21.7   4.4         7.6   13.8     2.0     16.1   
	NGC 6626 = M28      18 24 33  -24 52.2   6.9         6.9   12.0     1.5     15.7   
	NGC 6638            18 30 56  -25 29.8   2.6  7.3    9.2   15.0?    1.6:    15.9   
	NGC 6637 = M69      18 31 23  -32 20.9   4.9         7.7   13.7     1.8     16.0   
	NGC 6642            18 31 54  -23 28.5   2.9         8.9                    16.3   
	NGC 6652            18 35 46  -32 59.4   2.7  6.0    8.5   13.3     1.9     15.9   
	NGC 6656 = M22      18 36 24  -23 54.2    16         5.2   10.7     2.0     14.2   
	Palomar 8           18 41 30  -19 49.6   2.6        10.9   15.4             17.3   
	NGC 6681 = M70      18 43 13  -32 17.5   4.0         7.8   14.0?    1.2:    15.6   
	NGC 6712            18 53 04   -8 42.4   4.9:        8.1   13.3     2.0     16.3   
	NGC 6715 = M54      18 55 03  -30 28.7   4.1   12    7.7   15.2     1.3:    18.2   
	NGC 6717 = Pal 9    18 55 06  -22 42.1   2.7         8.4   14.0?    1.3:    15.6
	NGC 6723            18 59 33  -36 37.9   6.4   13    6.8   12.8     1.6     15.5   
	NGC 6749            19 05 15   +1 54.1         ~4   12.4:  16.5             19.7
	NGC 6752            19 10 52  -59 58.9    12   29    5.3   10.5     1.9     13.8   
	NGC 6760            19 11 12   +1 01.8   3.1  9.6    9.0   15.6             17.5:  
	NGC 6779 = M56      19 16 36  +30 11.1   4.4         8.4   13.0:    1.8:    16.2   
	Terzan 7            19 17 44  -34 39.5              12.0   15.0     1.6     17.9   
	Palomar 10          19 18 02  +18 34.3         ~4   13.2   18  ?            19.4
	Arp 2               19 28 44  -30 21.2        2.3   13.0   15.5     1.4     18.2   
	NGC 6809 = M55      19 39 59  -30 57.7   9.4   19    6.3   11.2     1.5     14.4   
	Terzan 8            19 41 44  -34 00.0              12.4:  15.0     1.5     18.0   
	Palomar 11          19 45 14   -8 00.4   5.0         9.8?                   17.3   
	NGC 6838 = M71      19 53 46  +18 46.7               8.4   12.1     1.9     14.4   
	NGC 6864 = M75      20 06 05  -21 55.3   3.2  6.8    8.6   14.6     1.8     17.5   
	NGC 6934            20 34 12   +7 24.3   3.0  7.1    8.9   13.8     1.7     17.1   
	NGC 6981 = M72      20 53 28  -12 32.2   2.9  6.6    9.2   14.2     1.4     16.9   
	NGC 7006            21 01 29  +16 11.3   1.4  3.6   10.6   15.6     1.7     18.8   
	NGC 7078 = M15      21 29 58  +12 10.0   7.7   18    6.3   12.6     1.4     15.8   
	NGC 7089 = M2       21 33 27   -0 49.4   7.3   16    6.6   13.1     1.6     16.1   
	NGC 7099 = M30      21 40 22  -23 10.8   5.3   12    6.9   12.1     1.5     15.1   
	Palomar 12          21 46 39  -21 15.1        2.9   11.7:  14.6     1.6     17.1   
	Palomar 13          23 06 44  +12 46.3        0.7   13.8:  17.0:    1.0:    17.7   
	NGC 7492            23 08 27  -15 36.7   0.3  4.2   11.2:  15.5:    1.3:    17.6   
	   
	
	==========
	
	
	Globular Cluster Bibliography and Notes
	version:  2 May 1999
	
	
	Name              References
	
	
	N 104=47 Tuc      Hesser & Hartwick 1977 ApJ Suppl 33,361; Alcaino & Liller
	                  1985 A&A 146,389
	N 288             Alcaino & Liller 1980 AJ 85,1592
	N 362             Harris 1982 ApJ Suppl 50,573
	Fornax-1          Buonanno et al 1985 A&A 152,65
	Fornax-2          Buonanno et al 1985 A&A 152,65
	N1049=Fornax-3    Buonanno et al 1985 A&A 152,65
	Fornax-4          Buonanno et al 1985 A&A 152,65
	Fornax-5          Buonanno et al 1985 A&A 152,65; mu25 diam from Grillmair,
	                  1998 Washington AAS meeting, HST obs
	N1261             Alcaino 1979 A&A Suppl 38,61
	Pal 1             Rosenberg et al. 1998 AJ 115,648 (no HB: prob an old open
	                  cluster)
	AM-1=E 1          Madore and Freedman 1989 ApJ 340,812
	Eridanus          Da Costa 1985 ApJ 291,230. Ortolani & Gratton 1989 A&A Suppl
	                  79,155 V(tip)=18.0/1.29
	Pal 2             
	N1851             Stetson 1981 AJ 86,687, Walker 1992 PASP 104,1063
	N1904=M79         Stetson & Harris 1977 AJ 82,954
	N2298             Alcaino 1974 A&A Suppl 13,55
	N2419             Racine & Harris 1975 ApJ 196,413
	Pyxis             da Costa 1995 PASP 107,937; Irwin+ 1995 ApJ 453,L21;
	                  Sarajedini+ 1996 AJ 112,2013.
	N2808             Harris 1975 ApJ Suppl 29,397; Alcaino & Liller 1986 AJ 91,87
	E 3               Gratton & Ortolani 1987 A&A Suppl 67,373. intermediate-age
	                  cluster?
	Pal 3             Ortolani & Gratton 1989 A&A Suppl 79,155
	N3201             Lee 1977 A&A Suppl 28,409
	Pal 4             Burbidge & Sandage 1958 ApJ 127,527; Christian & Heasley 1986
	                  ApJ 303,216
	N4147             Sandage & Walker 1955 AJ 60,230
	N4372             Hartwick & Hesser 1973 ApJ 186,1171; Alcaino & Liller 1986
	                  AJ 91,87
	Ru 106            Buonanno et al. 1993 AJ 105,184
	N4590=M68         Harris 1975 ApJ Suppl 29,397
	N4833             Menzies 1972 MNRAS 156,207
	N5024=M53         Cuffey 1965 AJ 70,732
	N5053             Sandage et al. 1977 AJ 82,389
	N5139=omega Cen   Cannon & Stobie 1973 MNRAS 162,207
	N5272=M3          Sandage 1953 AJ 58,61; Johnson & Sandage 1956 ApJ 124,379;
	                  center coords from Laget et al. 1998 A&A 332,93 from HST data
	N5286             Harris et al. 1976 ApJ Suppl 31,13; Samus et al. 1995 A&AS
	                  112,439
	AM-4              Inman & Carney 1987 AJ 93,1166. V(HB) is for m-s turnoff;
	                  intermediate-age cluster?
	N5466             Buonanno et al. 1984 A&A Suppl 56,79; Nemec & Harris 1987
	                  ApJ 316,172
	N5634             
	N5694             Harris 1975 ApJ Suppl 29,397
	I4499             Walker+ 1996 AJ 112,2026.
	N5824             Harris 1975 ApJ Suppl 29,397; Cannon et al. 1990 MNRAS
	                  243,151
	Pal 5             Sandage & Hartwick 1977 AJ 82,459
	N5897             Sandage & Katem 1968 ApJ 153,569
	N5904=M5          Arp 1962 ApJ 135,311
	N5927             Menzies 1974 MNRAS 169,79
	N5946             
	N5986             Harris et al. 1976 ApJ Suppl 31,13
	Pal 14            Harris & van den Bergh 1984 AJ 89,1816 (cen sfc br fainter
	                  than muV = 25.0). position from Archinal = GSC 0957-0359.
	N6093=M80         Harris & Racine 1974 AJ 79,472
	N6121=M4          Alcaino & Liller 1984 ApJ Suppl 56,19; Cudworth & Rees 1990
	                  AJ 99,1491
	N6101             Alcaino 1974 A&A Suppl 18,9
	N6144             Alcaino 1980 A&A Suppl 39,315
	N6139             
	Terzan 3          Barbuy et al. 1998 A&AS 132,333
	N6171=M107        Sandage & Katem 1964 ApJ 139,1088; Dickens & Rolland 1972
	                  MNRAS 160,37
	ESO 452-SC11      Bica et al. 1999 A&AS 136,363
	N6205=M13         Arp & Johnson 1955 ApJ 122,171
	N6218=M12         Racine 1971 AJ 76,331
	N6229             Carney et al 1991 AJ 101,1699
	N6235             Liller 1980 AJ 85,673
	N6254=M10         Harris et al. 1976 ApJ Suppl 31,13
	N6256             Alcaino 1983 A&A Suppl 53,47
	Pal 15            Harris & van den Bergh 1984 AJ 89,1816; Seitzer & Carney
	                  1990 AJ 99,229
	N6266=M62         Alcaino 1978 A&A Suppl 32,379
	N6273=M19         Harris et al. 1976 ApJ Suppl 31,13
	N6284             
	N6287             Stetson & West 1994 PASP 106,726
	N6293             Janes & Heasley 1991 AJ 101,2097
	N6304             Hesser & Hartwick 1976 ApJ 203,113
	N6316             Armandroff 1988 AJ 96,588
	N6341=M92         Sandage & Walker 1966 ApJ 143,313
	N6325             Harris 1975 ApJ Suppl 29,397
	N6333=M9          Janes & Heasley 1991 AJ 101,2097
	N6342             Armandroff 1988 AJ 96,588
	N6356             Sandage & Wallerstein 1960 ApJ 131,598
	N6355
	N6352             Fullton et al. 1995 AJ 110,652
	IC 1257           Harris et al. 1997, AJ 113,688
	Terzan 2          
	N6366             Pike 1976 MNRAS 177,257
	N6362             Alcaino 1972 A&A 16,220
	Terzan 4          
	Haute-Provence 1  Ortolani et al. 1997, MNRAS 284,692
	Liller 1          Ortolani et al. 1996, A&A 306,134
	N6380 = Ton 1     Ortolani et al. 1998, A&AS 127,471
	Terzan 1          
	Ton 2 = Pis 26    
	N6388             Alcaino 1981 A&A Suppl 44,33
	N6402=M14         Smith-Kogon et al. 1974 AJ 79,387
	N6401             
	N6397             Alcaino & Liller 1980 AJ 85,680
	Pal 6
	N6426             Zinn & Barnes 1996, AJ 112,1054.
	Djorgovski 1      
	Terzan 5          Ortolani+ 1996 A&A 308,733
	N6440             Martins et al. 1980 AJ 85,521; Ortolani+ 1994 A&ASuppl
	                  108,653
	N6441             Hesser & Hartwick 1976 ApJ 203,97
	Terzan 6          Barbuy+ 1997 A&AS 122,483.
	N6453             
	UKS 1             Ortolani et al. 1997, A&AS 126,319
	N6496             Armandroff 1988 AJ 96,588.
	Terzan 9          
	E456-SC38         Ortolani et al. 1997, A&AS 126,319
	Terzan 10         Ortolani et al. 1997, A&AS 126,319
	N6517             Harris 1975 ApJ Suppl 29,397
	N6522             Arp 1965 ApJ 141,43.
	N6535             Liller 1980 AJ 85,1480; Anthony-Twarog & Twarog 1985 ApJ
	                  291,595
	N6528             van den Bergh & Younger 1979 AJ 84,1305
	N6539             Armandroff 1988 AJ 96,588
	N6540             
	N6544             Alcaino 1983 A&A Suppl 52,105
	N6541             Alcaino 1979 A&A Suppl 35,233
	N6553             Hartwick 1975 PASP 87,77. Guarnieri et al. (1998 A&A 331,70)
	                  show that ground-based photom has serious zero-point offset
	                  due to crowding.  V(tip) and V(HB) derive from this newer
	                  analysis.
	N6558             
	I1276=Pal 7       Barbuy et al. 1998 A&AS 132,333
	Terzan 11         Ortolani et al. 1998, A&AS 127,471; approximate diameter 1'.5
	                  from estimate on V-band CCD frame.
	N6569             
	N6584             Alcaino & Liller 1985 A&A Suppl 62,317 
	N6624             Liller & Carney 1978 ApJ 224,383
	N6626=M28         Alcaino 1981 A&A Suppl 44,191; Rees and Cudworth 1991 AJ
	                  102,152.
	N6638             Alcaino & Liller 1983 AJ 88,1166
	N6637=M69         Hartwick & Sandage 1968 ApJ 153,715; Harris 1977 PASP 89,482
	N6642
	N6652             Ortolani+ 1994 A&A 286,444
	N6656=M22         Alcaino & Liller 1983 AJ 88,1330; Cudworth 1986 AJ 92,348
	Pal 8             Armandroff 1988 AJ 96,588
	N6681=M70         Harris 1975 ApJ Suppl 29,397
	N6712             Sandage & Smith 1966 ApJ 144,886; Cudworth 1988 AJ 96,105.
	N6715=M54         Harris 1975 ApJ Suppl 29,397; Sarajedini+ 1995, AJ
	N6717=Pal 9       Goranskii 1979 Sov AJ 23,284 (English translation);
	                  Hazen-Liller 1984 AJ 89,1551.
	N6723             Menzies 1974 MNRAS 168,177
	N6749             Rosino et al. 1997, MNRAS 289,745; Kaisler et al. 1997
	                  PASP 109,920
	N6752             Buonanno 1986 A&A Suppl 66,79
	N6760             Armandroff 1988 AJ 96,588
	Terzan 7          Buonanno+ 1994 ApJ 430,L121 and 1995 AJ 109,663
	N6779=M56         Barbon 1965 Asiago Contr no.175.
	Pal 10            Kailser et al. 1997 PASP 109,920.
	Arp 2             Buonanno+ 1994 ApJ 430,L121 and 1995 AJ 109,650
	N6809=M55         Lee 1977 A&A Suppl 29,1
	Terzan 8          Ortolani & Gratton 1990 A&A Suppl 82,71; Montegriffo et al.
	                  1998 MNRAS 294,315
	Pal 11
	N6838=M71         Arp & Hartwick 1971 ApJ 167,499 and Cudworth 1985 AJ 90,65
	N6864=M75         Harris 1975 ApJ Suppl 29,397
	N6934             Harris & Racine 1973 AJ 78,242
	N6981=M72         Dickens 1972 MNRAS 157,281
	N7006             Sandage & Wildey 1967 ApJ 150,469
	N7078=M15         Sandage 1970 ApJ 162,841; Buonanno et al. 1983 A&A Suppl
	                  51,83
	N7089=M2          Harris 1975 ApJ Suppl 29,397; Cudworth & Rauscher 1987 AJ
	                  93,856
	N7099=M30         Alcaino 1978 A&A Suppl 33,185; Alcaino & Wamsteker 1982
	                  A&A Suppl 50,141
	Pal 12            Harris & Canterna 1980 ApJ 239,815; Stetson et al. 1989 AJ
	                  97,1360
	Pal 13            Ortolani 1985 AJ 90,473
	N7492             Buonanno et al. 1987 A&A Suppl 67,327