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I'm working on psf-fitting the data from IRAC. DAOPHOT has a standard procedure of creating an empirical PSF from isolated field stars. But IRAC itself has a standard PSF (they call it PRF since it's location dependent) for each of its channel. Those PSF files are designed for IRAC's own data reduction software and are not compatible to DAOPHOT automatically. Since I want to compare the results given by empirical fitting and standard PSF provided, I need to implement those PSF's I downloaded from IRAC website into DAOPHOT.

I notice an earlier post discussed about this issue and it said I must do a pstselect to the standard PSF (a single source) to transform it into a readable file of DAOPHOT. This makes sense to me, but the result looks awkward (becomes not very symmetric).

I'm wondering if there's an alternative way to do this. Given that the standard PSF (r~20 pixels) is much larger than my targets (r~4 pixels), can it fit my targets? Does the size (in pixels) of sample stars/fitted PSF matter when perform psf-fitting in IRAF? Do I have to choose stars that are of similar luminosities to my target when performing pstselect? I'm new to IRAF/DAOPHOT so please give me some suggestions! Thank you so much!