Re: notes on the Iband phone conference

From: Lifan Wang (lifan@panisse.lbl.gov)
Date: Thu Jan 15 2004 - 16:30:28 PST

  • Next message: VAFadeyev@lbl.gov: "Re: notes on the Iband phone conference"

    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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