From: Serena Nobili (serena@physto.se)
Date: Tue Mar 09 2004 - 04:58:06 PST
Hi Chris,
I have build the Hubble diagram for each of the data sets separately, as
you asked. The results are not very different from what we already know,
within uncertainties, although as you said the Calan/Tololo show a slight
decrease in the weighted standard deviation (0.14 +- 0.06 instead of
0.16 +- 0.06)
First column is the dispersion about the fit made on each of the sets, and
the second column is the dispersion about the line fitted in the whole
set (column 5 of table 4 of the paper).
sigma_w sigma_w(paper)
CT 0.14 +- 0.06 0.16 +- 0.06
CfA 0.27 +- 0.06 0.27 +- 0.06
CfA2 0.15 +- 0.05 0.14 +- 0.04
Cheers,
Serena
On 3 Mar 2004, Chris Lidman wrote:
>>
>> >In relation to the numbered items.
>> >
>> >1) There was concern for the way the dispersion in the Hubble diagram
>> > is computed. Serena should compute the weighted r.m.s.
>> >
>> >Serena's reply ...
>> >
>> >I have done this. The weighted r.m.s. gives about the same values as
>> >the non-weighted r.m.s. due to the uncertainties, which are about the same
>> >for all the points. However, Table 4 now includes the weighted r.m.s. as
>> >well as the weighted average for each of the samples. I have also added a
>> >discussion in section 3 about the differences between the data sets.
>> >
>> >Chris' comment ...
>> >
>> >I think that we were also interested in seeing the RMS scatter about
>> >the individual Hubble lines and not the scatter about the Hubble line
>> >that is derived from the entire data set. Was the RMS calculated in
>> >this way? It is not 100% clear in the paper.
>> >
>>
>> I think the mean value of the residuals for each data set (column 4 of
>> Table 4) should be taken as an indication that differences are not
>> important. Although I could run the fit on each data set separately, I
>> don't think this is really relevant, given the low statistics of each of
>> them separately, e.g. only 6 SNe are in the CfA sample. For the same
>> reason I think any claims on differences between the data sets
>> (which I don't clearly see anyway), should be done very carefully.
>>
>
>Nevertheless, I think it should be done. I understand that the sample
>size is small, but I expect that you'll find that the RMS for the
>Calan/Tololo sample will show a significant decrease. I do not
>expect there to be much of a change for the CfA and CfA2 samples.
>
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