[vsnet-chat 4787] WZ Sge field calibration

[aah@nofs.navy.mil]

Arlo Landolt and I have been calibrating the bright stars
in the WZ Sge field.  After my first photometric night, I had
a suspicion that the values for the companions quoted in
Krzeminski and Kraft, 1964, ApJ 140, 921, either had to be
in error or else had larger error bars than they listed.
It was either that or my photometry was in error! (And you always worry...)
  Arlo has finished his calibration, and I list below the 4 relevant
stars along with my data, his data, and Kreminski and Kraft.
Star CS is the blue star about 45 arcsec south of comparison C,
which in turn is the brightest star in the field and a couple
of arcmin south of WZ Sge.  For each star, the first line is my
data; the second line is Arlo's values; the third line is from K&K.
  My data comes from 4 mostly photometric nights (not the best
that I have seen) with the NOFS 1.0m telescope and Tektronix
1024x1024 CCD.  In particular, star C, the bright comparison, is
near saturation and so has larger error than the other stars.
Arlo's data comes from 3 nights (2 observations/night) at CTIO using
a standard photoelectric photometer and with nonlinear transformation
coefficients.

ID    RA  (J2000) DEC      V     B-V    U-B    V-R    R-I    verr   bverr  uberr  vrerr  rierr
A  302.006040  17.669979  9.681  1.017  0.825  0.519  0.495  0.007  0.010  0.013  0.009  0.004
                          9.686  1.012 +0.780 +0.531 +0.488  0.005  0.002  0.007  0.003  0.004
                          9.72   1.03   0.76
                          
B  302.022582  17.617128 11.773  0.415  0.167  0.211  0.205  0.007  0.012  0.007  0.007  0.010
                         11.770 +0.393 +0.207 +0.215 +0.210  0.003  0.005  0.007  0.003  0.005
                         11.84   0.39   0.22
                         
C  301.890602  17.666824  8.728  0.160  0.107  0.065  0.061  0.013  0.012  0.029  0.011  0.014
                          8.737 +0.168 +0.136 +0.075 +0.078  0.005  0.004  0.006  0.002  0.003
                          8.76   0.16   0.13
                          
CS 301.889824  17.654468 11.769  0.184  0.120  0.073  0.078  0.010  0.012  0.018  0.009  0.009
                         11.755 +0.192 +0.150 +0.088 +0.113  0.005  0.006  0.005  0.003  0.007

Other than for the (R-I) color for star CS, Landolt and Henden agree
pretty well.  K&K appear to be about 0.04mag too faint at V (even more
for star B), but have good colors.  I think I need to work on my (U-B)
measures; a nonlinear transformation here might help.
  Bottom line:  the stars in the wzsge.bright.dat field photometry file
should be pretty close to the Landolt system, and you should use those
values (or Landolt's values for the stars listed above) in preference
to the ones in K&K.
Arne

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