[vsnet-obs 18107] Re: (fwd) SN1998es photometry and astrometry (Sala)

[bas@lowell.Lowell.Edu (Brian Skiff)]

     The USNO-A series magnitudes are usually somewhat too bright for both
the blue and red magnitudes, but there is wide variation from field to
field.  This is almost certainly the source of the problem with Dr. Sala's
SN magnitude.  In any case, without proper calibration directly in the
field, setting zero-points in unfiltered CCD images is not really possible.
Dr. Sala may wish to also image the nearby GSPC field (about 1.5 degrees
from the supernova), and compare the magnitudes he gets from 'Astrometrica'
with the true V and B-V values.  He may get a surprise!
     I am observing tonight at the Lowell 1.1-m telescope, and plan to 
obtain BVR photometry in the field of NGC 632 in a little while.

\Brian

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