NGC 5634 (GCL 28, H 70) Globular Cluster in Virgo

Located at: RA 14 hours 29 minutes 37 seconds, Dec -05 degrees 58 minutes 35 seconds

Size: 5.5' Magnitude: 9.5 Class: 4

North is up

West to the right

Telescope:

 8" f5 Newtonian reflector

Camera:

 ST-8XME, self-guided, binned 1x1, temp -15c, camera control MaxIm DL 4.53

Image:

 Red (Hoya 25A) filter, 100 minutes (10 x 10 minute subs), 06/4/2006

Processing:

CCDStack 1.1, Photoshop 7.0

Location:

 Rolling Roof Observatory, Thousand Oaks, CA 91360 (+34d 13m 29s -118h 52m 20s)

Notes: From the NGC / IC Project

Contemporary Visual Observation(s) for NGC 5634

NGC 5634
14 29 37.2 -05 58 35
V = 9.4;  Size 4.9

17.5": (4/13/96): fairly bright, moderately large, irregularly round, 3.5' 
diameter.  Contains a large bright core of 2' diameter which appears mottled 
with stellarings or knots.  The brightest knot is on the the NW side of the 
core.  Set in a striking field between mag 8.5 SAO 139967 1.4' ESE and a mag 11 
star 1.9' W with a mag 10 star 3.7' SW of center.

17.5" (6/8/91): bright, round, 3.5' diameter.  Situated in a pretty field among 
three bright stars.  The small halo smoothly increases to a broadly concentrated 
core which is very mottled but not resolved.  A few very faint stars are 
resolved off the edges of the halo at 412x and a star or knot is visible at the 
W edge of the core.

8": moderately bright, moderately large.  A mag 10 star is on the E edge and a 
mag 12 star on the W edge.

- by Steve Gottlieb
Historical Research Notes / Correction for NGC 5634
NGC 5634.  See NGC 5897. - Dr. Harold G. Corwin, Jr.

Historical Research Notes / Correction for NGC 5897 (red color mine)

NGC 5897 is H VI 8 as well as H VI 19.  JH noted the identification problem
with the stars observed in WH's Sweep 209 on 25 April 1784 (see CGH, p. 109), 
and Auwers and Dreyer have notes about the field [Dreyer's are in the NGC, p. 
223; IC1, p. 284 (combined NGC/IC edition of 1962); WH's Scientific Papers, 
Volume 1, p. 302; and MNRAS 73, 37, 1912].  (Marth apparently also published a 
note on VI 8 in 1864, but I have not seen that.)  None of these folks 
positively identified VI 8, the only non-stellar object seen in the sweep, 
though Dreyer mentioned the possibility of N5897 and was leaning toward N5634 
in 1912.

The confusion arose simply because 25 April was a poor night; WH noted "flying 
clouds and hazy" at the beginning of the sweep.  Nevertheless he, hoping to 
see more of the great "stratum" of nebulae that he'd found the previous 
months, swept for just over half an hour until he was completely clouded out.  
The entire sweep consists of four stars and one cluster.  Dreyer reproduces 
the sweep in the Scientific Papers:

   13h 57m   ..    ..    flying clouds and hazy
   14  01}
         }   62   1d19'  7.8m  
     -0.5}
     10.7    89   1 45   7m
     12.5     0     19   cluster ...
     25.2    59   1 16   star
     25.4   -16      4   6.7m
       31    ..    ..    cloudy

The first column is the clock reading.  Dreyer notes that WH reset the clock
after the previous sweep, and that there is an uncertainty of 11 or 12 minutes
in the readings.  The second column is not explained, but is apparently a raw
reading, approximately in arcminutes, of the relative north polar distance.  
The third column is reduced to relative north polar distance in degrees and
arcminutes, and the fourth gives notes and object descriptions.  So, the sweep 
consists of relative positions of four stars and one cluster.

WH's full description of the cluster clearly makes it a globular:  "A very
close, compressed cluster of stars, 8 or 9' in diameter, extremely rich, of an
irregular round figure, a little extended.  The stars are so small as hardly
to be visible, and so accumulated in the middle as to look nebulous."  

There are only three globular clusters in the right RA (14h to 16h) and Dec
(+5d to -25d) ranges:  NGC 5634, NGC 5897, and NGC 5904 (M 5).  None of the
historical sources mention NGC 5904, probably assuming it is too large and 
bright to have been WH's mystery object.  As I've noted, Dreyer seemed to 
favor N5634 over N5897.  However, N5634 is only half the size noted by WH, and 
has a bright star near to the southeast, and another even brighter star fairly 
close to the south-southwest.  WH would have noted these in any description 
that he made of the object (as he, in fact, did; see the GC and NGC 
descriptions for N5634).

This leaves NGC 5897 as the most likely candidate.  That it is indeed the 
correct object can be shown by reducing the relative clock times and polar
distances for the stars to absolute values, using the equinox 1784.32 position 
of the cluster as the origin.  That gives the following positions for 
equinoxes 1784.32 and (precessed to) J2000:

  RA (1784.32) Dec  RA (J2000) Dec       RA  (ICRS)  Dec       V       BD
   14 53.6 -21 12   15 06.0 -22 03   15 06 27.14 -22 01 54.6  6.14  -21 4030
   15 03.2 -21 38   15 15.7 -22 27   15 16 23.01 -22 23 57.9  5.52  -21 4065
   15 17.7 -21 09   15 30.2 -21 54   15 30 42.81 -21 52 42.8  7.80  -21 4128
   15 17.9 -19 57   15 30.3 -20 42   15 30 36.25 -20 43 42.8  6.21  -20 4246

I've added the Tycho-2 positions, the V magnitudes, and the BD identifications
to the table.  It's easy to see that WH's positions are systematically too
small in RA and too far south in Dec.  But if the systematic differences are
removed, the stars match the modern positions to within WH's usual errors (3-4
arcmin).  It's also easy to see the effect of the clouds on WH's magnitude
estimates, too.

Going through the exercise using NGC 5634 and M 5 as the origins shows that
they could not have been WH's cluster -- there are no stars near them matching 
the relative positions and magnitudes noted in the sweep.

Dreyer could have performed this same exercise with the BD (I used SAO and the
version of Tycho-2 online at CDS), but for some reason did not.  Since it is
an obvious check, and could easily have been done using the BD data, I wonder 
if anyone else has thought to do this over the years.

In any event, there is no doubt that NGC 5897 is the mystery object H VI 8.
 - Dr. Harold G. Corwin, Jr.