From: Chris Lidman (clidman@eso.org)
Date: Wed Mar 10 2004 - 05:24:51 PST
Dear Serena,
From Alex's plot, one gets a slightly different result in the
k-corrections when using different spectral templates. This was the
point that Peter had brought up several months ago when he was showing
that one could get systematic differences as large as 0.2 magnitudes
when using different templates.
This is an uncertainty which affects all SNe whether they are near
ones observed in the I-band or ones at z~0.5 observed in the J-Band.
I do not think that we can argue that the k-corrections for the z~0.5
ones are more uncertain than the low redshift ones. I'd argue that
they are equally uncertain. Currently, the paper suggests that the
k-corrections for distant SNe might be more uncertain.
The size of the systematic uncertainty is more difficult to judge.
On a case-by-case basis, the systematic uncertainty may be larger
(as large as the 0.2 magnitudes noted by Peter), but, for, most
SNe, the uncertainty is likely to be much less. I think that we
should note this in the paper by expanding the second paragraph in
section 2.2.
This does not affect your analysis nor your results, but I think
that the issue of uncertainty in the k-corrections needs to be
better addressed in the paper.
Cheers, Chris.
On Wed, 2004-03-10 at 09:13, Serena Nobili wrote:
> Hi Alex,
>
> thanks for checking this out. The difference you found using my templates
> are due to restframe/observed frame,i.e. I am using restframe dates. This
> makes our results coincide perfectly, which I believe is already a good
> point.
>
> For the difference you found between the results obtained using Rob's
> templates and mine, they agree with what have been already pointed out by
> Chris for K_JI. These differences are in fact within the quoted uncertainty
> of 0.05. I believe also that Rob's work in the I-band is probably not as
> accurate as in B,V and R, nor as in the Nobili et al. 2003 paper, since it
> was not a relevant band for the Knop et al paper (Rob, do you agree with
> this?). I any case, the quoted uncertainty (0.05) takes care of these
> differences, giving us confidence in what we are doing.
>
> I attach a plot where the K-corrections you computed are plotted versus
> restframe days. As you see the black and the cyan lines coincide, since
> they have both been computed using my templates. The red line instead is
> computed using Rob's template.
> Cheers,
>
> Serena
>
>
>
> On Tue, 9 Mar 2004, Alex Conley wrote:
>
> >Hello Serena,
> >
> > I have run my K-corrections on the same dates as yours, and I have to
> >report that I also get a rather different result than you do. This is
> >displayed graphically for the z=0.05 case in the first attachment (I got
> >the line styles wrong in the legend-- sorry). Shown are your values, my
> >values, and the values I get with my code and filter curves using your
> >uberspectra. The values that I get with your uberspectra are very similar
> >to yours. The difference is probably due to one or both of the following:
> > (i) I assumed that the dates were observer frame, and you used rest
> > frame.
> > (ii) I am using versions of Bessell's filters with the linear function
> > removed and you are not.
> >In any case, they are close enough not to worry about.
> >
> >The comparison with my K-corrections is not so close. The differences
> >are pretty substantial, with my K-corrections generally being smaller.
> >You shouldn't pay attention to dates past about 30 days because the color
> >model has run out of steam.
> >
> >The other attachment has the actual numbers for the three cases that
> >you gave, as well as a side by side comparison for z=0.05.
> >
> >Alex
> >
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