Mark's colour term plots

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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    colterm_i.ps.gz

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                        colterm_i.ps.gz
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    colterm_r.ps.gz

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                        colterm_r.ps.gz
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    colterm_z.ps.gz

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                        colterm_z.ps.gz
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                        Postscript Document (application/postscript)
                Encoding: 
                        BASE64