Description
Subject: more on synthetic colour terms
Date: Wed, 24 May 2006 10:45:36 -0400 (EDT)
From: Mark Sullivan
Hi,
OK, here's a better (i.e. debugged) analysis of the synthetic colour
terms. The plots show the synthetic colours calculated on the calspec
library (blue) and the Pickles library (red) stars. Overplotted are three
lines. They are:
- dashed (not a fit): The French colour term. This is calculated in their
document over the colour range indicated by the vertical solid lines.
- solid: A fit to all the stars
- Dotted: A fit to stars in the same colour range that the French used in
their analysis.
Results:
French Limited All
g -0.156 -0.158 -0.143
r 0.000 -0.019 -0.020
i -0.094 -0.086 -0.085
z 0.050 0.038 0.035
Note: Multiply by -1 to get these terms in the sense that you may be used
to!
Comments:
-) These synthetic colour terms are very close to those which the French
determine over the colour range that they used.
-) The colour terms can be quite different in some filters in other colour
ranges!
-) There's some evidence for slight nonlinear colour terms in g
-) There is probably a colour term in r. It would be worth repeating the
French analysis to confirm.
-) In i, if one fits colours at r-i>1.5, a steeper slope would be
obtained, which is what the French found. Hence, and offset moving the
x-axis right (i.e. if we're not exactly in the AB system) will bring us
into complete agreement with the French over that limited colour range
-) The z is a bit crazy. This could be because the star SEDs only go to
10000A whereas the filters go a bit further (about 5% of the SDSS-z filter
is at wave>10000A for example). I'll look for some stars defined further
into the red, but I don't know of that many. But note how different the
colour term would be using blue (calspec) stars!!
colterm_g.ps.gz
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colterm_g.ps.gz
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Postscript Document (application/postscript)
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BASE64
colterm_i.ps.gz
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colterm_i.ps.gz
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BASE64
colterm_r.ps.gz
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colterm_r.ps.gz
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BASE64
colterm_z.ps.gz
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colterm_z.ps.gz
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Postscript Document (application/postscript)
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BASE64