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Unformatted text preview: 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 • 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)How far out to count?...
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This note was uploaded on 11/09/2009 for the course AST 4762 taught by Professor Harrington during the Fall '09 term at University of Central Florida.
- Fall '09