From: Alex Conley (aconley@panisse.lbl.gov)
Date: Wed Apr 30 2003 - 14:41:25 PDT
One minor note of caution about your quote reguarding the CMAGIC
dispersion: 'which is able to standardize the vast majority of local
SNe Ia to within 0.08 mag (in contrast to ~0.11 mag which lightcurve...)'
(page 29, Apr 30 draft).
The dispersion quoted in the CMAGIC paper is a little different than what
people normally quote -- or at least what I've been told is what people
quote. What Lifan has provided is the weighted average of the dispersion
from the Hubble line. Peter claims that what people usually do is to try
to figure out what error to add in quadrature with the lightcurve error
bar to get a chisquare of 1 to the Hubble fit, which tends to result in a
considerably larger estimate of the dispersion. I haven't tried this with
Lifan's fits directly, but when I play with my own fits the values compare
as:
Weighted average: 0.1
Make chisquare 1: 0.17
Note that these values are larger than Lifan's because I haven't used
the host-galaxy extinction values from Phillips 99, which have a major
effect on the dispersion.
I don't think you should change anything in the paper, particularly
because this value plays such a minor part in your paper, but this is one
of those pieces of information to have in the back of your mind.
Alex
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