From: Serena Nobili (serena@physto.se)
Date: Fri Jan 16 2004 - 03:12:35 PST
Dear Greg,
I am glad you had the time to do this check. I don't really have time now
to un-dust what I did few months ago (perhaps 5 or 6 months), but it is
not impossible that I did something wrong at the time. I hope the
reduction of the HST data will confirm your result. In any case, I don't
think we can use the argument of stretch in B to decide which template is
more probable. For example, surpricingly, both 1999ff and 2000fr were
fitted by the template of 1992bc, but they have very different stretch in
B:
1992bc sb=1.076 sI=1.171
1999ff sb=0.820
2000fr sb=1.064
We can attempt comparing the Bmax you found in your fit for 1999Q, with
the luminosity distance they publish for it in the Tonry et al paper, to
check if we are at least on the same side of the Hubble diagram.
Unfortunatelly, as you said, sB=1 for 1999Q will not help decreasing the
dispersion in the Hubble diagram for the high-z SNe (in this sense finding
a low stretch would be better for us).
Cheers
Serena
On Fri, 16 Jan 2004, Greg Aldering wrote:
>
>Hi Serena,
>
>I've made a few notes based on further thinking and examination of
>the additional plots you have put on the webpage.`
>
>Based on your figures of Imax versus chi^2 for the three high-z SNe,
>and the 99Q fits for 89B and 99ac templates on your webpage, it is now
>more clear to me what issue we are dealing with. Namely, unlike the
>other two high-z SNe, the SN1999Q fits allow both 89B and 99ac
>templates at similarly good chi^2, and these give peak magnitudes that
>differ by about 0.2 mag (as you said in the telecon). This suggests
>that, baring other information, one has to take an uncertainty of 0.14
>mag (i.e., if the probabilty of 89B and 99ac are equal). One can use
>the relative chi^2 to weight by the relative chi-sqr to get an improved
>peak magnitude and uncertainty. (One might also consider the relative
>likelihood of a 89B versus a 99ac.)
>
>However, more can be done to try to determine whether 99Q is more like
>99ac or 89B in other respects. If you can rule out (or estimate relative
>probabilities) for 99ac or 89B as templates for 99ac then the
>uncertainty can be further reduced.
>
>I was able to fit a B-band lightcurve to the I + (B-I) data in Table 1
>of Riess 2000 and get a good constraint on stretch. I estimate that
>s = 1+/-0.05 based on a by-hand fit. I fixed the restframe dates wrt Tmax
>using the "Age" given in Riess' Table 1; the rationale being that Riess
>had other B-band data and so probably constrained the data of max fairly well
>(as we did for 00fr). I also assumed that since the published restframe
>B-band data were optical observations taken with HST, while the
>restframe I-band is from noisy NIR data, the correct errors on the
>I+(B-I) data points should be sqrt(sigma_BmI^2 - sigma_I^2). Under these
>assumptions (which give very small, ~ 0.05 mag, error bars for each
>point in B), I get excellent chi^2/DOF from my by-hand fits, with all
>points within 1-sigma (0.05 mag) of the fit. (An appropriately
>constrained fit in SNMINUT could firm up this numbers.)
>
>So let's compare 89B and 99ac with 99Q. Below are the stretches for each:
>
> 89B has s_B = 0.89 s_I = 1.10 (s_B based on dm15 = 1.31)
> 99ac has s_B = 1.079 s_I = 1.23 (outside calibration range)
> 99Q has s_B ~ 1 s_I = unknown
>
>It basically looks like 99Q has a stretch centered between these two.
>Perhaps its magnitude is between as well. However, my fit was rough and
>the stretch for 99Q could pull towards one or the other. After a better
>fit of the B-band lightcurve this question should be reexamined.
>(I originally started looking at this based on the low B-band stretch
>you found, but my fit doesn't support such a low stretch).
>
>Note that the fact that we can fit the stretch for 99Q further allows
>us to use stretch correction for the high-redshift SNe! As you have
>mentioned, this still may not improve the high-z Hubble diagram since
>99Q appears to be fainter than expected.
>
>Misc. coments:
>
> Figures 3 and 4 are just continuations of Fig 2, so shouldn't be new figures.
>
> I could not locate plots for SN 1989B through SN 1993O lightcurve fits
>
> The 42 I-band templates all have uncertainties versus time - have these
> been accounted for in high-z fits?
>
>
>I'm still sorting through some of the issues, but wanted to get the news
>of the B-band fitting to you. I'll send more later as things unfold.
>
>Cheers,
>
>Greg
>
>
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