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Hi everyone, I'm new to IRAF and now trying to perform PSF-fitting to a couple of white dwarfs that are blended with DAOPHOT package. I followed a few online tutorials to set up the parameters and used the ALLSTAR command at last. But a problem has existed for a long time. Although most of the small sources could be subtracted nicely, I kept getting dark cores for those larger sources in my field. Does anyone have an idea of what may cause this problem? Thank you so much!

I am not a DAOPHOT user but I can offer some thoughts which may have already. Are you sure the stars are not saturated or the stars used to create the PSF are not saturated. While the code may attempt to check this based on header or task parameters it is always possible these are not exactly right.

I hope this might help.

Frank Valdes