lect13 - UCF Physics AST 5765/4762(Advanced Astronomical...

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UCF Physics: AST 5765/4762: (Advanced) Astronomical Data Analysis Fall 2008 Lecture Notes: 13. PSF and Photometry 1 Check in: 2:00 — 2:10, 10 min Questions before we start? How was HW6 Reminder: solutions are in /home/ast5937/hw/hw * /hw * _sol Error in Howell: p. 79, it’s a (2 L + 1) × (2 L + 1) box, not an L × L box. 2 Point-Spread Function (PSF): 2:10 — 2:20, 10 min Atmosphere has cells of air w/ differing temperatures Cells refract light, also move High-speed images show stellar point source bouncing around Central limit theorem Gaussian Diffraction r D = 1 . 2 λ d (1) Telescope aberrations (astigmatism, coma, etc.) All these effects produce PSF Convolve “reality” image with PSF observed ds9 stars_13s_1_cor.fits , cuts in X and Y Why are bright stars bigger? Same PSF! Every image, and sometimes different parts of images, has a different PSF 3 Aperture Photometry: 2:20 — 2:30, 10 min Want to measure (relative) flux of stars Could just count all the DN, but some sky remains Do want all of signal, do not want to add noise 1
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lect13 - UCF Physics AST 5765/4762(Advanced Astronomical...

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