[vsnet-chat 2415] Re: [vsnet-chat] SN

[aah@nofs.navy.mil]

Jean marie Llapasset asked why photometric measurements
of SN1999em differed between raw measures and
subtracting out the background galaxy.  I'm a little
suspicious of the results presented using wavelets
to model the underlying galaxy since the difference
between this technique and the non-subtractive technique
is 0.7mag, which is exactly a factor of two and might
just be a numeric error.
  In general, most observers do not subtract the background
galaxy, but they should do so.  I stay clear of SNe
photometry because of this!  Usually if the SNe is bright,
or in a fairly uniform region of the galaxy, using a circular
aperture with a concentric sky annulus will subtract out
the galaxy pretty well.  If you want to understand
the correct techniques, look at Richmond, et. al.,
Astronomical Journal 109, 2121, 1995.
Arne

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