From: Lifan Wang (lifan@panisse.lbl.gov)
Date: Thu Jan 15 2004 - 16:30:28 PST
Dear Serena,
I think you wrote an excellent paper. I have yet to find some time
to check the I-band dispersions, although I feel strongly that 0.19m is
too large.
Please note that Phillips has published dispersion of 0.13m for a
sample of 15 supernovae when he set a Bmax-Vmax < 0.2 cut.
Cheers,
Lifan
On Thu, 15 Jan 2004, Serena Nobili wrote:
>
> 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/
> http://www.thehungersite.com/
>
-- Lifan Wang (510) 495 2733 (o) (510) 704 0119 (h)
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