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lect20 - UCF Physics AST 5765/4762(Advanced Astronomical...

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UCF Physics: AST 5765/4762: (Advanced) Astronomical Data Analysis Fall 2009 Lecture Notes: 20. Aperture Photometry 1 Check In: 10:30 — 10:35, 5 min Questions before we start? 2 Aperture Photometry: 10:35 — 10:45, 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 (Draw grid on board, put star in it) Establish center accurately Place aperture in GREEN Place sky annuli in RED Table: Light Area Bad Pixels (DN) (pix 2 ) Star F * N * must fix Sky F sky N sky don’t count Do not count bad pixels in sky region (why must count for star?) Aperture photometry equation: F * , cal = F * , raw - N * F sky N sky (1) Aperture correction W/ PSF. 3 Size of the Sky Annulus: 10:45 — 11:05, 20 min Draw Gaussian profile + sky, with noise Mark aperture locations in color Want all of starlight, but minimal sky noise 1
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Establish σ using bright star (why bright?) Use gauss2dfit or just do FWHM and convert Count DN within 3-4 σ from center for star Count DN in sky annulus further out, How far out to count? (radial profile) eog . S/N vs.
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