From: Alex Conley (aconley@panisse.lbl.gov)
Date: Thu Mar 13 2003 - 20:58:03 PST
I have finished checking the Hamuy and Riess SNe for fit stability. For
the most part they are pretty stable, with a few exceptions mostly having
to do with floating offset cases. In general, I think that sn1992ag is
the only SNe which floating offsets helped. All of the others mentioned
as needing the offsets don't IMHO. In fact, some of them are made much
worse by letting the offset float, both in terms of the visual quality of
the fit and that they go a bit unstable.
sn1995bd is a piece of crap, and I'm glad it's excluded.
My fit strategy was to do fit I with the defaults, fit II with the initial
conditions matching the fit values from I fairly closely (I find that this
frequently leads to better error bar estimates), and in fit III I try to
'shake things up' to see if anything changes. For the SNe listed as
needing floating offsets, there are fits IV and V (and sometimes VI) where
I continue the process with floating offsets.
These labels are also attached to all of the output plots.
Note that the magnitudes in Rob's tables have been corrected for
extinction, but mine haven't, so it takes a little work to compare them.
The stretches are directly comparable. All of the fits were done with
the latest version of snminuit. The corrected magnitudes are known to
have bad error bars, but Rob doesn't use those since he is fitting his
own alpha anyways. In fact, I can't imagine any reason why anybody would
ever use them directly.
Attached are three things:
(i) a gnumeric spreadsheet giving details of many of the fit parameters
for each SNe. The fit description is either 'basic fit' or gives
changes relative to the basic fit. The basic fit is detailed below.
(ii) A tar file with all of the snminuit control files used to do these
fits.
(iii) A tar file with all of the output from snmin02.
These will dump a bunch of files in your current directory if you untar
them, so you might want to do this in a temporary directory.
The basic fit uses the defaults
1 't of B max' 0.0 0.2
2 'Stretch ' 1.0 0.02 0.45 5
3 'Vert scl 1' 0.7 0.05 0.1 10
4 'Vert off 1' 0.0 0.05
5 'Vert scl 2' 0.7 0.05 0.1 10
6 'Vert off 2' 0.0 0.05
Now, on to the 42 SNe. I expect these to be much more unstable.
Alex
Here are SN by SN comments:
sn1990o -- solid
sn1990af -- solid
sn1992p -- solid
sn1992ae -- solid
sn1992ag -- ugly fit, moves around. Fitting with floating offsets (fit
IV)
makes it much better
sn1992al -- solid
sn1992aq -- solid
sn1992bg -- values solid. Improving initial guess inflates error bars
slightly
sn1992bh -- solid
sn1992bl -- solid
sn1992bo -- solid. Rob has this as one that requires floating offsets.
Fits IV and V are floating, I-III are not. The differences are pretty
minor (0.03 mag, 0.02 stretch in the direction that they will mostly
cancel each other).
sn1992bp -- solid. Another floating offset. This time the effect is a
little larger. As before I-III are fixed, IV and V are floated.
sn1992br -- solid
sn1992bs -- solid
sn1993b -- pretty solid. Very minor (3rd decimal place) shifts in the
error
bars when you tweak. Rob has this as an SNe which require floating
offsets,
but I don't really see it. Nonetheless, fits IV and V show what
floating
offsets do. Floating offsets make a substantial difference
sn1993o -- solid BUT not a great fit to B peak. Changing it to floating
offsets doesn't help. Either way, the fit parameters are pretty
insensitive
to the initial values.
sn1993ag -- solid
sn1994M -- solid
sn1994S -- pretty solid, but the V peak seems slightly off. Changing to
floating offsets doesn't really improve this. In any case, changing the
initial conditions changes the error bars a bit, but not the central
values.
sn1995ac -- solid
sn1995bd -- a piece of junk. The fits move around a bit when the initial
conditions change, but mostly this just misses the peak badly, even when
a floating offset is used. I'm glad this one gets excluded from the
fits.
sn1996C -- solid. There are some points around max (one point especially
in B)
which aren't fit so well, but playing around with the fit doesn't seem
to
help.
sn1996ab -- solid as fixed, not solid as float. This is one that Rob
claims
needs a floating offset. I don't agree. Furthermore, I think that the
floating fits suck, and it was a mistake to use them. The fixed floats
are
quite stable, and the floating ones move around a decent amount when you
adjust your initial conditions.
sn1996bl -- solid
sn1996bo -- solid, both fixed and floating. However, the floating fit is
worse. It seems to miss the peak. Again, using floating offsets has
ruined a perfectly good fit.
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