PSF-photometry

Philip Willemsen wrote on Nov 07, 2002

Dear IRAF-users,
I want to do psf-photometry on crowded fields. I find that (though the Psf
model is quite good) the star-subtraction always results in deep
holes (e.g. -4000 to -6000 counts for a star which had a peak of about 25000
counts!). I tried various (annulu,dannulu) values in the phot-run and
also various combinations of (psfrad,fitrad), but this
does not change the results much. Does anybody know what's going wrong?
Thank you.

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Mike Hudson wrote on Nov 07, 2002

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-- 
Mike Hudson
Dept. of Physics             Tel: +1-519-888-4567 x2212
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Waterloo, ON N2L 3G1         http://astro.uwaterloo.ca/~mjhudson

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Phil Massey wrote on Nov 07, 2002

Needless to say, if the PSF really **is** quite good, you
shouldn't be left with deep holes.  Do you see the same problems
on the PSF stars themselves in the subtracted images?

The exact values for psfrad and fitrad are relatively irrelevant, 
as long as they are sent to sensible values.

You might want to compare your parameters against those described in the
"Guide to Stellar Photometry with IRAF" (Massey & Davis).

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Last post on Nov 07, 2002