From: Serena Nobili (serena@physto.se)
Date: Thu Jan 15 2004 - 05:06:07 PST
Dear SCPers,
I would like to thank you for the discussion on the I-band paper. Though
at the end of the two and half hour phone conference I was too tired to
make sense of it, I think it was very useful.
I wrote a short note to summarize what it was said. For brevity sake I
only wrote what I think were the most important points about science. The
observations made on the presentation are not reported here (but I will
eventually consider them in the paper). I also tried to remember all the
must-do and who was appointed to them. Moreover I gathered some quick
answers to a couple of points. If you see I forgot something important,
please feel free to point it out.
Cheers
Serena
Notes on the phone conference (Jan 14, 2003)
by Serena Nobili
--------------------------------------------------------
1) Discussion about what is the minimum redshift to be put in the
Hubble diagram (HD) as I originally put z > 0.01. Did we agree on z >
0.015 as in Knop papers? This choice would cut 6 out of 28 SNe.
2) The dispersion measured as r.m.s. by me in the I-band HD after stretch
correction is 0.19. Lifan gets 0.11- 0.12 as weighted standard deviation
when using Dm15 for calibration. I have computed the weighted standard
deviation in my case, but I get the same answer, since the errors are very
small. Note that the r.m.s. in the full Calan/Tololo sample, for dm15
correction, published by Hamuy et al. is about 0.13 mag. This is
consistent with my result, obtained using a sub-sample of the
Calan/Tololo, within error bars (0.15 +-0.02).
3) On the extinction correction of 1998es and 1999dq and their being
intrinsically redder, there a couple of things to check, a) uncertainty in
velocity =600 km/s instead of 300 km/s, b) k-corrections, since Rollin
suggested that 98es has a broad double Ca IR feature. Note that the cut in
redshift at 0.015 would exclude these two SNe anyway, in which case it is
not relevant for this paper. Can we have the spectrum of 98es to check the
k-correction?
4) sb vs si plot. I believe we decided not to show it, or if we do,
then we refer to Wang et al (2004) for further discussion. To see the
plot:
(seventh plot, or page 13 of the ps file)
http://www.physto.se/~snova/internal/papers/iband/figs/select.comp_ib.ps
5) Spectral templates: Nobili vs Knop templates. Differences in
K-corrections from J-band to rest frame I-band are about 0.05 mag. This
is very small and it is not limiting the analysis presented in this
paper.
6) Definition of J band photometric system: 0.05 mag systematic
uncertainty estimated by Chris Lidman by comparing the Person J to
Bessel and Brett J. See document linked Chris'web page for discussion
(usual SCP username and passwd):
http://www.sc.eso.org/~clidman/kcorr.ps
7) Stretch or Dm15 unknown for 1999Q (Riess' supernova). It has been
suggested (by Saul) that Vitaly looks at the HST data which are
public, and fit its rest frame B-band light curve. This should take a
couple of days only (plus time for problems which will naturally
occur).
8) Estimate of systematic uncertainty on the high-z light curve fit. Greg
Aldering expressed his worry for over-estimating the one on 1999Q (which
is about 0.18 mag). I pointed out than the case of 99Q is the only
one in which 2 templates give a similar chisq for the fit and the fitted
Imax differs by about 0.2 mag. We discussed this by looking at the plot in
the paper web page, which shows the Imax fitted versus chisq of the fit,
for the 42 templates:
http://www.physto.se/~snova/internal/papers/iband/figs/read_fitlog.ps
I now made available in the web page a plot to show the best fit and
second best fit templates with the data of SN 1999Q:
http://www.physto.se/~snova/internal/papers/iband/#hizsys
9) Greg Aldering expressed his worry again for the case of 1999Q in
the analysis of Section 6 (colors and grey dust). We discussed the
reasons why we get different results than Riess for the test on grey
dust based on B-I colors. These are the correlation between the data
of the same SN, the different B-I versus time used in our analysis,
the different K-corrections, and the fact we assume stretch=1 for
it. Knowing the stretch of this SN would help in feeling more
confident (see point 7 above). Greg also worries about the correlation
between colors at different epochs, calculated in Nobili et al
2003. It has been proposed for people to read the paper. Also, Greg
needs to think about it and perhaps suggest tests or plots which would
make him more confident in the analysis. Ariel pointed out that Riess
claims this SN to be too blue, but we don't see that in Figure 16 of
the paper.
----------------------------------------------------------------------
www.physto.se/~serena
Tel +46 8 55378661
Give free food at:
http://www.porloschicos.com/
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