[vsnet-chat 2389] sn1999em field photometry

[aah@nofs.navy.mil]

Yamaoka-san has given GSC cross-id's for the stars
in common between the AAVSO, VSNET and Henden fields.
I've had a photometric night and have recalibrated
the field using all-sky photometry.  I get the following
for Yamaoka's list (zero point errors ~0.015):
GSC_ID    VSNET AAVSO   V     B-V    V-R    R-I
4739-0111 1240  134   12.926  0.734  0.402  0.389
4739-0434 1262  124   12.405  1.202  0.662  0.605
4739-0235 1470  149   14.890  0.795  0.449  0.426
 --       1539  156   15.677  0.671  0.394  0.413
4739-0125 1260  130   13.015  1.157  0.622  0.553
4739-0012 1401  139   14.329  0.663  0.381  0.352
4739-0155 1344  144   13.789  0.841  0.494  0.432
4739-0459 1330  142   13.601  0.875  0.524  0.492
4739-0598 1388  138   13.904  0.720  0.432  0.411
                112   10.769  0.414  0.268  0.268

The supernova is at 04:41:27.15  -02:51:45.4
(J2000, USNO-A2.0, err +/-0.2arcsec) and was at
V=13.8 on 991104.

The calibrating star for my first list was 4739-0434.
This star may be slightly variable
since my all-sky results are 0.04mag fainter than
the L&V value.  Also, my rough transformations for
(V-R) and (R-I) were incorrect by about 0.1mag.  I took
a short exposure set to check the Tycho star to the
north of the galaxy; it is much brighter than the catalog value.
  I've placed the new photometry at
http://ftp.nofs.navy.mil/pub/outgoing/aah/sequence/sn1999em.dat
(note that it contains UBVRI measures; I wouldn't trust
(U-B) for stars fainter than V=17.)
Bruce Sumner has offered to create a sequence for this
field, which I assume will be similar to Berto Monard's
sequence.  In any case, I think we now have a reasonable
set of stars for following the supernova.
Arne

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