From: Alexander Conley (AJConley@lbl.gov)
Date: Tue Nov 09 2004 - 11:27:59 PST
As you all know, one of the things that makes me the most
unhappy about the current analysis is the difference between
the mean residual of the Knop and Barris sample.
A number of things have changed in my analysis since I did
these calculations, so I felt it was time to revisit them. Most
significantly, a change in the fitting procedure (starting/ending
dates in stretch for CMAG region) eliminated one of the Barris
SNe and added a different one. Exchanging 1 out of 24 SNe
didn't have much effect on the cosmology fit, but it may have a
larger effect when comparing two samples of 5-6 SNe.
So I recalculated the various quantities, and the good news is
that the significance of the difference has been reduced slightly.
As things now stand, the Knop sample is 0.26 mag dimmer than
the Barris sample. If extinction correction is applied this shrinks to
0.09 magnitudes.
Estimating the significance of this difference is a bit messy. The
range of photometric errors and the intrinsic dispersion complicate
things. Therefore I ran a Monte-Carlo where I generated a large
number of realizations of both samples and used this
to calculate how frequently the two samples would differ by this much.
In any case, the difference before extinction correction is 2.28 sigma,
and after extinction correction is 0.78 sigma.
It doesn't radically change the story, but is worth noting.
Alex
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