From: Saul Perlmutter (saul@lbl.gov)
Date: Sat Mar 27 2004 - 20:46:19 PST
...I spent some time talking to Lifan about this last week, and as I
understand it he is using each individual supernova's (U),B,V, R, I
photometry (whatever is available) for the particular day of the
spectrum to correct its spectrum on that day. So he says that he
gets the same color when he synthetically integrates over the R or I
band for Rob's template or Serena's template or for the particular SN
he is working with (and he repeats this for a large number of different
supernova's spectra for the same epoch), but he get's different K
corrections. If this is right it would presumably be because the
excess signal in the uberspectrum is adding equally to the R and to the
I band so that the color stays the same, but the K correction sees the
excess signal.
I asked him to send these 1-D spectra for a couple example
supernovae, so that someone else could verify that they agree on both
the points above. (Any other ideas for how to get to the bottom of
this quickly?) --Saul
Robert A. Knop Jr. wrote:
On Sat, Mar 27, 2004 at 11:46:11PM -0400, Chris Lidman wrote:
The 0.1 magnitudes comes from Lifan's analysis of ~500 spectra - no
don't jump! I am assuming that Lifan got this part of the analysis
correct. The 0.05 magnitudes we had used before came from comparing a
much smaller number of spectra, basically yours and Rob's. I feel that
the 0.1 magnidues estimated by Lifan is more secure estimate of the
scatter.
Did Lifan give that scatter, or is that based on an offset between Lifan
and what Serena did?
Before I'd trust this at all, I'd want to know more about Lifan's
analysis.
For instance, from what I know about what he's done, it's entirely
possible that he's taken a supernova spectrum and applied a reddening
law to get the B-V color right. (This is the sort of thing that Peter
used to do.) In other words, any continuum calibration out in the R and
I may be extrapolated, with a potential corresponding increase in
scatter. Until I know more about what Lifan did, I don't even want to
trust that part of the analysis. His estimate could be an overestimate.
Now if he did do something careful to maintain continuum levels in R and
I, then, sure, that part of the analysis may be fine. But I haven't
seen nearly enough about his analysis to believe that yet.
-Rob
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