[vsnet-chat 1623] Re: [vsnet-chart 134] Chart of SN1999X

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

     Since Mike Schwarz' latest supernova is fairly faint, most of the
magnitude observations will be via CCD.  I compared available photometric
sequences in the relevant POSS field against USNO-A2.0 magnitudes, and find
that a small zero-point adjustment is needed to obtain standard R from the
USNO-A2.0 'mr' magnitudes.  These run systematically about 0.2 mag. too faint
in this field, so adjust unfiltered CCD magnitudes derived from A2.0 data
by -0.2 to obtain standard R magnitudes.  Be sure to use as many A2.0 stars
as can be measured reliably on your frames in order to beat down the noise
in this calibration.
     Incidentally, the "Kato V" derived from the A2.0 blue and red magnitudes
for the same calibration stars comes out about right for standard V in this
field, but is somewhat noisy.  Again, use a lot of stars---not just one---to
make estimates using these derived magnitudes.

\Brian

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