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Comma indicatior (was New PC-IRAF Release)



> 
> While you are looking it over, is there anything in IRAF that offers
> measurements of coma? We need some numbers and common terminology to
> discuss coma in a consistent and useful fashion. It would also be
> another encouragment for me to use it.
>

This is a good question.

Maybe the ratio of the sum of the counts inside a 2 x PSF
aperture over the counts inside a 1 x PSF aperture.

The problem is that this would also measure trailing, poor focus
and bad seeing.  Maybe you take the above and normalize it so
that the result is always 1.0 for a central star. The result would
be a "blurryness ratio" that is relative to the image center.
I think if you plotted "blurryness ratio" v. distance from center
you see a steep curve for TASS Mk IV images.  We could talk about
steepness or range of the curve as a comma indicator.

Didn't Michael do something like this already?  He looked at
the effect of aperture size across an image.  The above is
about the same thing.

I think you could do the above with IRAF or likely many
other systems as well.  IRAF is both an interactive system
and a programming environment.  I think the way many people
use IRAF is to use it interactively until they understand
the problem then write a script.  

-- 
  Chris Albertson

  calbertson@logicon.com                  Voice: 626-351-0089  X127
  Logicon, Pasadena California            Fax:   626-351-0699