From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Sat Mar 22 2003 - 09:28:01 PST
Every lightcurve fit I've done uses the new templates. The only things
that don't are the contours taken from the old paper. (I did refit the
cosmology there, but used the old gersontable.)
> 3) In the "Differences" table is the "chirat" column the ratio of the
> SNminuit lightcurve fit Chi-squares?
"Differences" is always stroked-filled, unless I screwed up in which
case it's the opposite. The ratio is stroked/filled, and is the ratio
of the chisq/dof column from the gersontable. Note that in line A-5,
it's a werid comparison, since I'm comparing the joint fit chisquare to
the chisquare from the second stage of a two-stage fit. (The main
difference, though, is that there are two more degrees of freedom when
you let the zero float.)
To compare the effects of only fixing the MW extiction, compare the
stroked lines of A-2 and A-1. That worsens the chisquare from 57 to
59.2. The sequence of stroked fits from lines A-1 to A-3 gives you the
sequence of chisquares. (Then add line A-5 for the simultaneous fit
method; skip A-4, as that's playing with different K-corrections.)
> I do note that between the P99 fit of line A-1, and the full treatment
> you would like to use on A-5, the *change* in Chi-squared is 8.2. Since
> the *change* in Chi-squared is a useful means of hypothesis testing, we
> see that the final A-5 fits are almost 3-sigma worse that the original P99
> fits.
I've put residuals online.
I'm not convinced your interpretation of the chisquare change makes
sense. Yes, adding 6.63 to the minimum chisquare *of a given fit* gives
you the location of the 3-sigma contour. It's not obvious to me that
similar sorts of subtractions of chisquares of different fits to
different sets of data can be similarly interpreted.
In any event, any such micromanaging of the chisquares of the fits is
tantamount splitting hares while being faced by a hungry lion. We can
change the chisquares of the fits by as much or even more more than
these sorts of differences just by choosing which errors to use on our
supernovae (e.g. by changing the assumed alpha for erorr calcluations,
or using redshift errors). This also changes the difference between the
P99 chisquare and the chisquare from my new fits. See:
http://brahms.phy.vanderbilt.edu/~rknop/scp/hst/#screwingaround
*Now* can I move on?
...unless we want to sit around and worry about the fact that doing the
fits with what is probably a better set of errors (i.e. mostly from not
overestimating the alpha we can use in propogating dstretch into our
magnitude error bars) has a goodness-of-fit of only about 0.002,
irrespective of whether you use the P99 gersontable or my new lightcurve
parameters.
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
This archive was generated by hypermail 2.1.4 : Sat Mar 22 2003 - 09:28:03 PST