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lect22 - UCF Physics AST 5765/4762(Advanced Astronomical...

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UCF Physics: AST 5765/4762: (Advanced) Astronomical Data Analysis Fall 2009 Lecture Notes: 22. Aperture Photometry 1 Check In: 10:30 — 10:35, 5 min Questions before we start? 2 Go over HW7: 10:35 — 11:05, 30 min 3 Convolution: 11:05 — 11:15, 10 min Convolution describes signal spreading (among other things) PSF Divide signal into discrete points Multiply each point by a function Replace point with function, shifted to location of point ( f * g )( t ) integraldisplay -∞ f ( τ ) g ( t - τ )d τ = integraldisplay -∞ f ( t - τ ) g ( τ )d τ (1) ( f * g )( n ) summationdisplay m = -∞ f ( m ) g ( n - m ) = summationdisplay m = -∞ f ( n - m ) g ( m ) (2) Demo movies In astronomy, kernel often symmetric Used for smoothing Can be calculated fast with Fourier Transforms, but don’t, use np.convolve() 4 Extended-Source Photometry: 11:15 — 11:25, 10 min Galaxies, nebulae, planets are not point-like 1colliding.jpg Galaxies: fit laws to radial dropoff in brightness 2spiral.jpg Find 50% enclosed light radius 3elliptical.jpg
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