From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Thu Mar 11 2004 - 04:57:05 PST
On Thu, Mar 11, 2004 at 01:35:44PM +0100, Serena Nobili wrote:
> I have done some checks now. You are perfectly right about the difference
> in K-corrections. I tell you what I think the story is. Both Rob and I
> have started with the spectral template provided by Peter, and modified
> its colors according to our (different) studies of average color
> evolution. I did not modify the B-band color, but only V,R and I. Rob did
> modify also the U-band. I believe this is the origin of the discrepancy. I
> attach a plot to illustrate this. Both Rob's and my template at day 0 are
> plotted together with the restframe B-band and the red-shifted (z=0.05)
> one, and with the restframe U-band. As you see the two templates differ
> most in the blue edge of the B-band filter, where there is some influence
> of the U-band. This means that Rob's template should be used any time the
> U-band could play any role (even marginal) in the computation of
> K-corrections. If you trust one of the two method for estimating the color
> evolution more than the other, then you should use the corresponding
> template. However, I think in general they are both valid and I don't see
> mine as better than Rob's (or viceversa), unless it involves the U-band.
> This is why I decided to add an uncertainty on the K-corrections in the
> paper where only I-band is involved. K-corrections are still an open
> issue, I am afraid.
> I really hope this will help the discussion.
I'll agree with all this.
For reasons Serena and I both articulated before, Serena's template is
probably better when you're dealing with the I-band, which is what is
relevant for this paper.
But Peter's U-B colors are too low to the tune of at least 0.2
magnitudes, and given that I'd say that even any time you're in the
B-band you'd be better off using a template which was colored taking
into account this U-band issue.
This isn't a worry for this paper, but of course all of it is a worry
for the group as the decide how to do further K-corrections.
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
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