PSF Subtraction in DAOPHOT
josephmeiring wrote on Jul 29, 2009
Hello,
I'm working on some PSF subtractions with DAOPHOT, and have seen that when ever I run PSF and interactively subtract the PSF from a star in the image (with 's' during the PSF routine), it seems to work fairly well. When I run substar however, the output images look god-awful, mainly the brighter stars have circular regions around them where it is oversubtraced and much more noisy than the sky is in the original image. It seems like a sky fitting issue, am I right? So:
1) What are reasonable values for the sky fitting parameters. The field is not very crowded, but deep, with 0.154" pixels and 0.8" seeing. THere are about 6-8 decent stars for PSF modelling.
2) What are optimal daopar parameters for the fitting radius and radius of the PSF model?
3) A pure analytical function does not work at all as the PSF, the subtraction is really bad. With varorder=1 I can get a better subtraction. What exactly are these lookup tables described in the help file, and what are the residuals in the PSF image? Do these residuals stay constant for every star that is getting subtracted, or do the residuals get fit for every subtraction?
4) There is really only one star that I need to PSF subtract. Is there some way to get a model PSF with the residuals for only this star (not the residuals from all the stars that were used in the PSF fit ), so that I can run that through something like IDP3 in IDL for more interactive PSF subtraction?
Many Thanks!
I'm working on some PSF subtractions with DAOPHOT, and have seen that when ever I run PSF and interactively subtract the PSF from a star in the image (with 's' during the PSF routine), it seems to work fairly well. When I run substar however, the output images look god-awful, mainly the brighter stars have circular regions around them where it is oversubtraced and much more noisy than the sky is in the original image. It seems like a sky fitting issue, am I right? So:
1) What are reasonable values for the sky fitting parameters. The field is not very crowded, but deep, with 0.154" pixels and 0.8" seeing. THere are about 6-8 decent stars for PSF modelling.
2) What are optimal daopar parameters for the fitting radius and radius of the PSF model?
3) A pure analytical function does not work at all as the PSF, the subtraction is really bad. With varorder=1 I can get a better subtraction. What exactly are these lookup tables described in the help file, and what are the residuals in the PSF image? Do these residuals stay constant for every star that is getting subtracted, or do the residuals get fit for every subtraction?
4) There is really only one star that I need to PSF subtract. Is there some way to get a model PSF with the residuals for only this star (not the residuals from all the stars that were used in the PSF fit ), so that I can run that through something like IDP3 in IDL for more interactive PSF subtraction?
Many Thanks!
Last post on Jul 29, 2009