From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Thu Apr 01 2004 - 15:37:12 PST
On Thu, Apr 01, 2004 at 03:29:09PM -0800, Lifan Wang wrote:
> I might have found the reason for the difference between my K-corr and
> the Serena's. In my fit, I only normalize the spectra to the observed
> magnitudes close to the region of interest, and use a smooth function for
> the normalization. When I try to include all the colors, I do end up
> something closer to what I can get from Serena's template, but I think
> this is unphysical.
???
How can that be unphysical?
What's happening is that your smooth function is unanchored when you
don't use the other colors, and you're getting a different continuum
from what Serena is getting. I don't see how that could be unphysical;
it simply sounds like a matter of whether or not you're consistent with
the observed data.
> Note that contrary to what's in Rob's email, that in my approach, I did
> not "applying the function that pushes it a little up here, a little down
> there, in comparison to what Serena did".
>
> The normalization function I use has NO wiggles, and as it seems, we all
> agree that this is important.
That's not what I meant. *ANY* normalization that isn't a single
constant is going to push the spectrum up a little in one place, down a
little in another. This isn't wiggles, this is just what you have to do
if you're normalizing more than one color.
It's probably possible that there are degeneracies-- that two different
normalization functions could yield the same photometry. This is
another reason to have as many photometry poitns as possible. (Indeed,
we'd be better off if we had Z and J photometry to anchor the spectrum
to the red of the I-band.)
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
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