From: Greg Aldering (aldering@panisse.lbl.gov)
Date: Fri May 02 2003 - 17:32:20 PDT
Hi Rob,
As both Reynald and I have raised some questions about the R-band
ground-based lightcurve points relative to the HST points, I went
through the lightcurve plots and tables to try to identify any
common denominators that might point to a problem. Here I give
a rough fractional flux offset of the ground-based data near
peak relative to the fitted lightcurve (that is, roughly the amount
by which the lightcurve should be scaled to match the ground-based
data near peak), along with the source(s) of the ground-based data
near peak.
SN % error Source
---------------------------------------
97eq +10% WIYN
97ek +10% BTC & WIYN
97ez +15% BTC
98aw 0% BTC & WIYN
98be +10% BTC
98ay +15% BTC
98ax 0% BTC
98as 0% BTC
98bi +10% BTC
00fr 0% Keck & NTT
It is disturbing at the flux errors are all in the sense of the
ground-based data being to bright. The size of the scaling is troubling
as well - it is often much larger than the assigned photometric
calibration errors would indicate. The fact that several SNe are
perfectly fine suggests the problem is not with the HST R-band
zeropoint (common to all the HST data).
I understand that correlated errors also come into play, and that the
photometric calibration could have come from telescope other than those
listed. The sources of calibration should probably be tracked down, to
see whether our photometry has an Achilles heel.
It appears that the ground-based data have relatively little weight
relate to the HST points, so if there is a problem, it probably won't
change our results all that much. However, a reviewer may well hold us
up because of this.
Note that all the I-band lightcurves look fine.
Any suggestions for things to look at? Do all the zeropoints need to be
checked for a bad calibration?
- Greg
This archive was generated by hypermail 2.1.4 : Fri May 02 2003 - 17:32:41 PDT