[vsnet-alert 10435] Re: outburst of a recurrent nova in M31!

[Brian Skiff]

>>  LGGS_J004252.55+411613.2 V=21.946 B-V=0.002 U-B=0.306 V-R=0.835

>>  The last object = LGGS_J004252.55+411613.2 is remarkably blue 
>>  among them, and the positional difference is 1.9 arcsec
>>  (a bit too off?)

     Where I have been able to make comparisons against UCAC2 and
2MASS, Phil Massey's LGGS astrometry is fairly good, with external
errors of around 0".25 for reasonably isolated stars (at the 
scale of the KPNO 3.8-m mosaic camera images).  This field is very
much in the bright part of the nuclear bulge of M31, so there could
be much larger errors due to sheer crowding.
     I note that uncertainties on the photometry for this star
are substantial (~0.2 - 0.3 mag in each color), and indeed the
three colors shown above are non-physical.  Basically you can't
get an ordinary star to come out with those colors no matter what
the reddening or H-alpha emission is (or two stars for that matter).
Since this is a very crowded place and the star (or catalogue entry)
is rather faint, the combination of crowding and photometric errors
are likely to be responsible for the nonsense colors.

\Brian