From: Greg Aldering (aldering@panisse.lbl.gov)
Date: Tue Oct 22 2002 - 14:42:05 PDT
FYI,
With the help of Mark Sullivan I was able to lay my hands on our HST
STIS Snapshot images of the host of SN 1997ai / 9779, coadd the images,
and photometer the host galaxy. The host galaxy is R = 24.9 +/- 0.1,
and would be unresolved from the ground (it is roughly 0.6" x 0.4" FWZI).
The presence of a non-negligable host matters in this case because we
never took final refs for this SN, and in P99 we reported its
lightcurve parameters based on an SNMINUIT with a floating baseline.
The baseline value was -0.12 (in relative flux units where the SN peak
brightness is nominally 1); the physical interpretation of this would
normally be that we had oversubtracted host light. In this case, since
no host was subtracted, the SN is reported as 0.12 mag too bright
because of the baseline. It is reported another 0.14 mag or so too
bright because the host light was included in the photometry points.
Assuming that the baseline and host errors weren't compensated by
stretch or some other aspect of the fit, this means that SN 1997ai was
reported as 0.26 mag too bright in P99.
- Greg
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