ASTRO 480- IRAF TUTORIAL Exercise 2

As tronomy 480 - IRAF Tutoria l and Exerci se VIntroduction to DAOphotPSF fitting and DAOphotAdvantages to PSF fittingThe original motivation f or psf fitting m ethods was f or crowded f ield photometry , w here often stellar i mages are blended, and any reasonable s ize aperture might include m ore than one star. DAOphot was d eveloped by Peter Stetso n at the Dominion Astrophysical O bservatory, Victoria B C, for precise ground-based photometry in the crowded f ields of globula r clusters. It h as s ince been incorporated into I RAF a s the PS F f itting package there. I f you w ant to know all the gory d etails see Stetso n (1987). Howev er, even for uncrowded environments psf methods may still y ield improved s ignal- to- noise- >10% co mpared to aperture photometry, since m ore of the available information i s b eing used. Th e profiles of stars from the grou nd have been found to c onsist o f an approximately Gaussi an core, due to s eeing (which m ay w ell vary), plus large w ings decreas ing only a s an inverse square in intensity, largely a result of atmospheric scattering o ff dust and a erosols, plus d irt and scratches in the optical s ystem. U se of profile fitting techniques can remov e mo st of the variations due to seeing changes, as w ell as enabling larger e ffective radii to be used.Procedure (in DAOphot)Here i s a summar y o f the procedure one must follow . 1) Find all the stars on the frame above a user set brightness ...