log space, various

We decided to simplify Ben Johnson's calibration code by switching the spectroscopic likelihood function to log space, where the calibration vector is additive. This makes the noise non-Gaussian, of course, but at very high signal-to-noise (where he is working), the Gaussian approximation is not severe. At Milky Way group meeting, Wilma Trick (MPIA) talked about observational signatures of spiral structure in the kinematics of gas and stars, and Alexia Lewis (UW) talked about the star-formation histories of patches of M31 from PHAT data. Her method is very simple (fitting the distribution of main-sequence stars); it could be applied to the Hipparcos data on the local neighborhood, which would be super-cool.

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