From: Serena Nobili (serena@physto.se)
Date: Fri Jan 16 2004 - 05:48:55 PST
Dear Lifan,
one problem could be in the stretch-Dm15 relation. If I am not wrong, both
Phillips and you use Dm15, instead I use sB. One way to go, since we are
using the "same" data set is to compare the fitted Imax. If you send me
the values you fitted for the Imax, I can do the comparison, or you could
compare them yourself if you prefer. Thus we will know if the problem is
in the fitted Imax of in the intrinsic difference between stretch and
Dm15, or something else.
Cheers
Serena
On Thu, 15 Jan 2004, Lifan Wang wrote:
>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/
>>
>
>
------------------------------------------------------------------------ www.physto.se/~serena Tel +46 8 55378661
Give free food at: http://www.porloschicos.com/ http://www.thehungersite.com/
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