From: Serena Nobili (serena@physto.se)
Date: Fri Jan 30 2004 - 07:11:38 PST
Hi Lifan,
did you have any chances of doing this check? If you don't have time now,
I could do the checks myself if you send me the Imax you fit on the
data. Thank you.
Cheers
Serena
On Fri, 16 Jan 2004, Serena Nobili wrote:
>
>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
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