2008-02-08

chi-squared fitting

I worked out derivatives and second derivatives of chi-squared as a function of date to analyze some of Barron's results in the blind date paper. Basically, as you might expect, the information in a single star increases with the magnitude of its proper motion and decreases with the uncertainty with which it has been measured. Duh! There are some subtleties in the limit that all the stars in the field are moving in the same direction, or in the limit that there are very few stars, or for stars which are large outliers in position. Barron made some plots to check my analysis and we may be close to converging.

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