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HiJust want to do a double check if my procedure is acceptable!I am doing fast photometry on a variable star - problem is that the field I am working in is relatively sparse. My CV is at 11-12 mag, while the only comparison stars bright and stable enough is at 14,15.7,15.9,16.2 mags.I construct a PSF using the comp stars - because the PSF constructed including the CV results in a swop of the lightcurves - "The comp stars varies and the CV is stable".I did use normal AppPhot, but the errors in the comp stars was too large. PSF gives me a more stable comparison normalization curve and smaller errors.Task and method:Use master.coo file and master.pst file and the use daophot tasks (in sequince - with relevant input in a script - some small stuf in between)
aphot
psf
allstarDump the .als files results to file and work from there.Q! Is the above method acceptable - or is the comp stars to "low" for accurate PSF measurements. When checking the .sub.fits frames there is some small bit of leftover counts for the CV, but it is around the sky-noise region?I would appreciate some recommendations and help.Regards
Pat

Hi,I am not a photometry expert but what you describe is reasonable. My only comment is that since you have a sparse field and a relatively bright target source a large aperture should get photometry to the same level of accuracy. As I understand your concern, the comparison sources produce larger scatter with aperture photometry. Of course this could be because they are faint but it could also be that you are not using a large enough aperture to avoid seeing effects.I hope this is of some help.Frank Valdes