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I am trying to perform psf photometry on a crowded field using the IRAF Daophot package, but I am running into a problem. I am not going about the standard procedure of creating a psf from my image since there are not enough "good" stars to create the psf with. Rather, I am using a high quality psf which was created from many images and is completely empirical (i.e., the psf has no analytical core unlike the psfs one creates using daophot). When I try to run the allstar task, using this psf, I encounter an error of the form ERROR: Image header parameter not found (FUNCTION).What happens next is that I edit the header file of this psf to include these parameters (which are not originally there) that are normally contained in the header file of the psf made using daophot; one by one, I get another error message stating that a certain parameter is not found. The thing is, I do not know certain parameters of my new, empirical psf that the header file needs, parameters such as PSFHEIGHT, PSFMAG, NPSFSTAR, etc. Is there any way to make the IRAF daophot task allstar work with an entirely emipircal psf? Or is there some way I can add in an analytical core to make this work? Or I am best off creating a psf from scratch (which I wish not to do)? Thanks.Josiah

I have the same problem exactly. Anybody got a fix?[quote:52a361bb67="jwalton"]I am trying to perform psf photometry on a crowded field using the IRAF Daophot package, but I am running into a problem. I am not going about the standard procedure of creating a psf from my image since there are not enough "good" stars to create the psf with. Rather, I am using a high quality psf which was created from many images and is completely empirical (i.e., the psf has no analytical core unlike the psfs one creates using daophot). When I try to run the allstar task, using this psf, I encounter an error of the form ERROR: Image header parameter not found (FUNCTION).What happens next is that I edit the header file of this psf to include these parameters (which are not originally there) that are normally contained in the header file of the psf made using daophot; one by one, I get another error message stating that a certain parameter is not found. The thing is, I do not know certain parameters of my new, empirical psf that the header file needs, parameters such as PSFHEIGHT, PSFMAG, NPSFSTAR, etc. Is there any way to make the IRAF daophot task allstar work with an entirely emipircal psf? Or is there some way I can add in an analytical core to make this work? Or I am best off creating a psf from scratch (which I wish not to do)? Thanks.Josiah[/quote:52a361bb67]

My knowledge of this is limited to remembering that's it's been discussed before in old mail, and you might find the answers there. See for examplehttps://iraf.net/phpBB2/viewtopic.php?t=82574&highlight=psf+function
https://iraf.net/phpBB2/viewtopic.php?t=82746&highlight=psf+functionThe 'Forum Search' button on the menubar will search archived messages.
-Mike

If you want to feed an external PSF into DAOPHOT you must first convert it into a DAOPHOT-type PSF. In other words, treat the external PSF file as an image file, even though it only contains 1 single "star"! This is trivial. Run daofind (optionally), phot, pstselect (optionally), and psf on it. You now have the same PSF information in the form that DAOPHOT can use e.g. in allstar. The only thing to watch out for is to make sure that you use the same phot parameters (zeropoint, aperture, annulus, exptime) on your PSF image as you did for your crowded field image - you must ensure that the same quantity of flux corresponds to the same instrumental magnitude in each. Otherwise, if there is a mismatch, allstar will get off to a bad start in scaling the PSF model flux to the initial .mag values of the crowded field stars.

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Dr. Ray Butler School of Physics (Lecturer) | Centre for Astronomy National University of Ireland - Galway, Ireland