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# lect16 - UCF Physics AST 5765/4762(Advanced Astronomical...

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UCF Physics: AST 5765/4762: (Advanced) Astronomical Data Analysis Fall 2008 Lecture Notes: 16. Extended-Source Photometry and Atmospheric Calibration 1 Check in: 2:00 — 2:10, 10 min Questions before we start? How was HW7? Who has read what? Quiz next Thursday unless all have read everything by Tuesday Reminder to take good notes in class for homework 2 N -Dimensional Gaussian: 2:10 — 2:20, 10 min We often use a 2D Gaussian to model a stellar PSF Usually symmetric, needn’t be Consider p G = 1 2 πσ 2 e 1 2 ( x - x 0 σ ) 2 (1) Integrates to 1. For 2D function, y direction must integrate to p G ( x ) at each x . Since p G integrates to 1, just multiply: p G ( x ) p G ( y ) This smears x Gaussian in y . Repeat for higher dimensions p G,N = N productdisplay i =1 1 radicalBig 2 πσ 2 i e 1 2 N i =1 parenleftBig x i - x i, 0 σ i parenrightBig 2 (2) Note exponent now looks like an ellipse, hence name elliptical Gaussian. See gaussian.py in class Python dir. 3 Extended-Source Photometry: 2:20 — 2:30, 10 min Galaxies, nebulae, planets are not point-like 1colliding.jpg Galaxies: fit laws to radial dropoff in brightness 2spiral.jpg 1

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Find 50% enclosed light radius 3elliptical.jpg Use standard stars to estimate flux per DN Convert images to magnitudes per sq. arcsec (basically take log & scale)
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