Hi,I'm an undergraduate student I'd like some help with PSF in special backgrounds.I'm having problems with photometry in RY tau.It has some nebulosity, which is not symmetrical.The filters are UBVRI.All things here are from V filter. [img:a12489b0df]http://perso.orange.fr/pgj/ry-tau.jpg[/img:a12489b0df]Larger http://antwrp.gsfc.nasa.gov/apod/ap050923.htmlOther stars near it have some nebulosity too.Ry tau's surface plot shows a greater slope near that dark strip.After psf subtraction, I get a "crater" with negative and positive peaks inside(some are near -500 and +1000 counts).I don't know exactly how much it interferes in Ry tau's profile, because other stars near it have similar asymmetrical profiles wihout showing nebulosity(in the frame).The star is with 32000 counts at its peak.The typical fwhm on the frame is around 1.8.I've tried different groups of psf models - the ones with symmetrical profile(but they were fainter and a little far from Ry tau) and the stars near Ry tau:Symmetrical - Phot's chosen aperture was 13(tested).It was chosen as psfrad too.As recommended on Lindsey Davis 94 DAOPHOT guide, fitrad was set to 3.Three PSF stars were chosen (varorder=0).This was made first to take the analytic function.Gauss seems to have the bet subtraction, so it was used.Asymmetrical - Same aperture and psfrad.The fitrad was chosen 1.8 because the radial profile shows a "step" of less than a hundred counts near 1.8 for these stars, and I wanted to avoid it.Four PSF stars were chosen.Allstar was used.I've started with fitrad 1.8 for allstar because of that step, but I've tried from 1.5 to 3.0.The result was not very different in both groups - the crater's depth increased with fitrad.None of the fitrad resulted in a smooth subtracted frame.The crater follows the nebulosity, having less counts near the dark strip than the opposite side. So I'd like to know if there some way to deal with this.Searching for IRAF stuff involving nebulosity I've found this :
http://www.adass.org/adass/proceedings/adass99/P2-21/
Plucy and cplucy tasks.I was not "officially" introduced to these tasks and I don't know if I got their purpose.Can they help me?
Thank you.