lect09 - UCF Physics AST 5765/4762(Advanced Astronomical...

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UCF Physics: AST 5765/4762: (Advanced) Astronomical Data Analysis Fall 2008 Lecture Notes: 9. Fitting and Astronomical Measurements 1 Check in: 2:00 — 2:10, 10 min Questions before we start? 2 Fitting Basics: 2:10 — 2:20, 10 min Have a set of theoretical equations, or a model . Some parameters are known, some are not. Unknowns are called free parameters . Want to find values of the free parameters so the model fits the data as well as possible. MUST have more data points than free parameters! Can estimate both parameters and their uncertainties, if enough data. Generally use maximum likelihood to decide which model is best (least squares is a special case). Sometimes can be done with minimization calculus, other times must be done numerically (see Bevington Ch. 8). There are Python routines for line fits and for generalized fits. Often problems can be reduced to or approximated by line fits. Always check goodness of fit, not just errors! 3 Linear Fitting: 2:20 — 2:45, 25 min Model: y = a + bx , measurements ( x i ,y i ) . Assume uncertainty σ i , mainly in y (or flip).
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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.

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lect09 - UCF Physics AST 5765/4762(Advanced Astronomical...

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