[vsnet-chat 856] PSF-fitting or aperture photometry (Richmond)

[Taichi Kato <tkato>]

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Date: Wed, 29 Apr 1998 23:36:45 +0900 (JST)
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To: Gianluca Masi <gianmasi@fr.flashnet.it>
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Subject: [vsnet-chat 0] Re: PSF-fitting or aperture photometry
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  Gianluca Masi asks:

>   As you know, there
> are two main ways to do astronomical photometry, using a CCD camera:
> aperture and PSF photometry. I was wondering which is the best one when
> the telescope used to capture the star light has a short focal lenght (1
> meter, for example), with a typical FHWM of 1.5-2.0 pixels. PSF fitting
> maybe difficult, considering such a small FWHM.

  Three points favor aperture photometry:

      1. if the PSF has FWHM 1.5-2.0 pixels, it is undersampled,
         and determining a good model for it will be difficult;
         by the same token, most of the light will fall within
         the central few pixels, making aperture photometry efficient
     
      2. the density of stars is, I would guess, going to be low
         unless you take long exposure and/or point towards the galactic
         plane

      3. aperture photometry is a lot simpler to perform, especially
         if you wish to work in automatic or semi-automatic mode

  The only situations where PSF photometry is really necessary are

      - very crowded fields
      - close binaries
      - point source embedded in nebulosity (SN in galaxy) ....
            and even PSF photometry isn't perfect for this job

  Good luck.

-- 
-----                                      
Michael Richmond                   "This is the heart that broke my finger."
mwrsps@rit.edu                     http://p674p06.isc.rit.edu/richmond/

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