From: Serena Nobili (serena@physto.se)
Date: Tue Feb 24 2004 - 06:39:34 PST
Dear collaborators,
I apologies for the delay in sending out this notes. I had a couple of
busy weeks, having to hand in my PhD thesis, but this is now over and I
can focus more on the paper.
Below is a list of points that were discussed during the meeting. I have
been working on them and plots and discussions are available on
the paper web page (see links and comments below).
Please, feel free to tell me if you think I forgot something.
Cheers
Serena
LINK TO THE PAPER WEB PAGE:
http://www.physto.se/~snova/internal/papers/iband/
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1) There was concern for the way the dispersion in the Hubble diagram
is computed. Serena should compute the weighted r.m.s.
I have done this. The weighted r.m.s. gives about the same values as
the non-weighted r.m.s. due to the uncertainties, which are about the same
for all the points. However, Table 4 now includes the weighted r.m.s. as
well as the weighted average for each of the samples. I have also added a
discussion in section 3 about the differences between the data sets.
2) Lifan computes different K-corrections than I. We should try to
compare them and figure out why there are differences. Serena uses
the spectral templates published in Nobili et al 2003. Lifan uses a
sample of nearby spectral templates for which he computes the
K-corrs and average them out. Lifan will try to compare them.
As Ariel pointed out, we would like to use templates for computing
K-corrections, as this is used for the high-z SNe, in order not to
treat them differently.
3) Peter raised the point of the K-correction for peculiar SNe (see
Peter's email in the archive of 12 Feb). Serena will plot the
peculiars with different symbols in the plots.
In the paper web page, there is the Hubble diagram where the peculiar SNe
are plotted with different symbols:
http://www.physto.se/~snova/internal/papers/iband/index.new.html#HD
In the same page. there is also a plot of B-band stretch factor versus
redshift, where the peculiars are again plotted with different symbols.
4) Serena will produce a plot of Bmax-Vmax to check how colors look
like for 1998es and 1999dq.
This is also there now. They look very normal:
http://www.physto.se/~snova/internal/papers/iband/index.new.html#hgext
5) Some concern again about the differences found in the 3 low-z
samples. One point was about the change in the I-band filter they
used at CFA that happened in 1998. Serena will check the residuals
the 6 SNe from the Jha (CfA2) sample to see if they have a
different behavior.
There are no trends or differences in their behavior. Check it:
http://www.physto.se/~snova/internal/papers/iband/index.new.html#HD2
6) There is the need to check the K-corrections for 2 of high-z SNe, in
particular for SN1999ff (sB=0.82).
Chris has checked this, confirming that the difference between the
K-corrections computed using my template and Rob's template agree within
0.05 mag. Meanwhile, as Ariel and I have been asking Brian Schmidt to
check the K-corrections in the paper by Tonry et al. 2003, we have finally
got news from him saying that their K-corrections in the paper are wrong.
Those were computed from the HST filters to the restframe I-band, instead
of the J-band to I-band. Note that he says also that the luminosity
distances in the paper are correct, since they did not use these
K-corrections but the fit of MLCS instead. This should help explaining in
the paper the large differences found. This concern only Tonry paper.
For Riess' K-corrections the problem is different, since the same value
was applied (by him) to all epochs (from restframe day+5 to day+46)
7) Chris has estimated corrections to be applied to the IR data (the 3
high-z SNe) in order to account for the discrepancy between the
Persson system (in which the SNe were calibrated) and the Bessel &
Brett system (see email by Chris in the archive of Feb 11). The
corrections (to be added) are 0.036 +- 0.012 mag with 0.02 mag
systematic uncertainty. If no corrections are applied then the
systematic uncertainty is 0.05 mag.
Latest calculations show that there is no systematic uncertainty on the
correction (see Chris email from Feb 20 2004 in the archive for details).
8) There was again concern about the way the systematic uncertainty on
the Imax fitted on the high-z SNe was estimated. There will be some
discussion added in the text to help clarify these worries.
A discussion about this has been added in the text of section 4.4.
9) It has been pointed out that one of the high-z SNe, SN 1999ff, is
fitted by the template with a very different B-band stretch. Serena
will check whether constraining the fit to templates with similar
B-band stretch as the high-z SN give very different results.
This is not the case. Templates with very different sB, give a similar
Imax. I found no trend in this. Please check plots and discussion in:
http://www.physto.se/~snova/internal/papers/iband/index.new.html#hizfit
A short discussion has been added in the paper.
10) Serena will try to add the restframe B,V-band for 1999Q, reduced by
Vitaliy, in the analysis presented in Section 6.
This is interesting! It turned out that the fit obtained by SNMINUIT
fixing the time of B-maximum to Tonry value, would give a color excess
E(B-V) = 0.2 mag (see email by Vitaliy in the archive on Feb 12). Given
that this SN is host-less, this value is very surprising. I have been
playing with numbers and plots. If the B-band stretch factor was sB=0.82
the colors would make perfectly sense (even in I-band). Unfortunately the
stretch fitted by SNMINUIT is 1.061 instead. Check plots and discussion
in:
http://www.physto.se/~snova/internal/papers/iband/index.new.html#99q
Giving all of this, I do not think we should add the B-V colors of SN1999Q
in the analysis of section 6.
11) We will also add some discussion about the low dependence of the
analysis on the correlation, and the chisq values reported in
Table 12 should not be reduced chisq.
This has been added in the discussion of Section 6, and Table 12 is
updated.
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www.physto.se/~serena
Tel +46 8 55378661
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