[vsnet-chat 2563] Re: NSV 4189

[Brian Skiff <bas@lowell.edu>]

     The GSC field around NSV 4189 was taken from a IIIa-J plate, so as a 
result, the GSC magnitudes are closer to blue magnitudes than visual or V.
The Guide Star Photometric Catalogue sequence S633 is about a degree away.
Here are positions and BV data for these stars:

Name       RA  (2000)  Dec    s     GSC       V    B-V    mGSC  delta
S633-A   8 39 50.5  -15 30 25 G  6011-0751   9.58  0.41   9.86  0.28
S633-B   8 39 55.6  -15 09 23 G  6011-0775  10.21  0.97  10.92  0.71
S633-C   8 40 23.9  -15 27 23 G  6012-0402  12.08  0.36  12.32  0.24
S633-D   8 39 32.1  -15 24 23 G  6011-0537  12.77  0.85  13.39  0.62
S633-E   8 39 54.0  -15 28 20 A             15.07  0.62  
S633-F   8 39 38.8  -15 28 11 A             15.65  0.81  

The last two columns show the GSC magnitudes and their difference from V.
There is clearly a color term in relation to the V magnitudes, since the two
somewhat blue stars have a smaller offset than the other stars.  Since the
region is at about 15 deg galactic latitude, I would expect the redder stars
to dominate a random sample.  Thus your best bet (lacking a proper sequence)
would be to use the GSC stars in your field as you are now, but make the
magnitudes brighter by 0.6 mag.
     Hope this helps.

\Brian

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