220  V2756 SAGITTARII   (ZAND)   Range: 13.0v-<15.2p
     Position:   18 14 34.50  -29 49 23.1 (J2000, from .dat file)
     Magnitude:  V=12.998  B-V=0.992      (in .dat file)

ID     RA  (2000)   DEC       X    Y   N    V      ERR     B-V    ERR 

a) Comparison star sequence

1    18 14 10.8  -29 53 22  -308 -239  2  10.056  0.062   0.941  0.011   
2    18 14 35.7  -29 48 00    16   83  2  10.729  0.045   1.734  0.026   
3    18 14 37.3  -29 44 11    37  312  2  11.497  0.031   0.382  0.025   
4    18 14 59.4  -29 44 49   325  274  2  11.742  0.038   0.317  0.028   
5    18 14 37.3  -29 46 36    36  167  2  12.121  0.044   0.359  0.021   
6    18 14 53.1  -29 44 47   242  276  2  12.569  0.034   0.625  0.027   
7    18 14 20.1  -29 47 29  -187  114  2  13.048  0.034   0.822  0.018   
8    18 14 32.8  -29 46 55   -23  148  2  13.509  0.037   0.579  0.028   
9    18 14 26.1  -29 46 50  -110  153  2  13.948  0.042   0.729  0.032   
10   18 14 31.6  -29 47 52   -37   91  2  14.104  0.039   0.707  0.023   
11   18 14 51.1  -29 47 12   216  131  2  14.420  0.018   0.918  0.030   
12   18 14 38.6  -29 49 17    53    6  2  14.812  0.027   1.046  0.000   
13   18 14 33.6  -29 50 41   -11  -78  2  15.141  0.039   1.006  0.044   
14   18 14 35.1  -29 49 57     8  -34  2  15.458  0.049   0.970  0.023   
15   18 14 35.0  -29 49 40     6  -17  2  16.801  0.043   0.951  0.059   


b) Wide-colour extension for CCD calibration

     18 14 37.6  -29 54 09    40 -286  2  13.599  0.054   1.362  0.025   
     18 14 32.0  -29 48 50   -32   33  2  13.585  0.034   1.819  0.015   
     18 14 25.1  -29 46 24  -122  179  2  13.843  0.046   1.901  0.026   


Notes:

1. The five brightest stars in this sequence are all saturated. 
However the first two stars do have reliable Tycho-2 magnitudes: 
star #1 V=9.91+/-0.05 and star #2 V=10.53+/-0.08. Note that star 
#2 is quite red, and is only included in the sequence because of 
its proximity to V2756 Sgr.

2. There is another bright Tycho-2 star at 18h 15m 05.1s -29d 49' 23' 
with V=6.80+/-0.01 and B-V=1.52. This star is also a Hipparcos 
micro-variable, and has been designated as NSV 24342 with a range 
of 6.78-6.84H and an approximate period of 0.04 days.

3. Star #4 has a photoelectric measure, when it was measured by 
Kilkenny, Publ. VSS RASNZ No. 11 1983 as part of the sequence for 
VZ Sgr. 

                Henden        Kilkenny
                   V     B-V      V     B-V
                 11.742 0.317   11.727 0.315

4. V2756 Sgr has two close companions for which care must be taken 
not to confuse them with when the variable is faint. An example 
of such confusion is in IBVS 469 where V2756 Sgr is stated to have 
a minimum of 15.2p as determined from an examination of 350 small 
scale Maria Mitchell plates. It is obvious that this magnitude is 
erroneous as it refers to the brighter of the two close companions, 
which has a blue magnitude of B=14.81. The companions are:

a) V=14.098+/-0.036  B-V=1.712+/-0.021 located 10 arcsec east of variable  
b) V=14.994+/-0.021  B-V=1.432+/-0.018 located 15 arcsec west of variable 

  
Bruce Sumner
22 April 2001