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Re: Coma, work to date



Hello Mark IV Coma Fans,

    Herb has raised some excellent issues!! While muddling along trying to get IRAF
installed (so that I can get rid of the hot-pixels that we have been talking about).
Then to process the set of images that Tom has sent me several weeks ago.....

    While busy with the above activities I began to wonder if we might use Mike G's
"FlatComp" program (suitably modified) to compensate for coma and other effects in
Mark IV images?? It uses a number of zones in Declination (usually eight) to produce
correction factors based on magnitudes of Tycho stars in each band to adjust the
photometric magnitudes and thus (possibly) compensate for the change in PSF's across
the image due to "coma" and other effects.

    It seems that this might be an area to look at applying to Mark IV images. It has
certainly worked well on Mark III images and could "hide a multitude of sins" in Mark
IV images, since as Tom has pointed out most of us will not have dark skies (such as
Arne has) and will have many effects (like coma) that we will want to remove from Mark
IV images (just as we did Mark III images).........

Glenn G.



Herbert R Johnson wrote:

> So that is the trouble with qualitative, or even one-valued, methods.
> Let me be plain, apparently my comments have not been clear. Then I'll
> mention what has been done, and ask "what's next?"
>
> Coma is a fixed function of the optics. It is therefore repeatable
> and to some extent consistent (one hopes). It is not desirable. So,
> *IF* it is desirable to compensate for coma, we need a method to characterize
> it sufficiently so that an algorithm - a program - can be constructed
> to do so. Waving a hand and making general statements about coma does
> not directly lead to either measuring it or compensating for it.
> It informs us of a problem, but not of a solution.
>
>