dust structures, code audit

At Milky Way group meeting, Eddie Schlafly (MPIA) showed beautiful results (combining PanSTARRS, APOGEE, 2MASS, and WISE data) on the dust extinction law in the Milky Way. He can see that some of the nearby dust structures have anomalous RV values (dust extinction law shapes). Some of these are previously unknown features; they only appear when you have maps of density and RV at the same time. Maybe he gets to name these new structures!

Late in the day, Ness and I audited her code that infers red-giant masses from APOGEE spectra. We found some issues with sigmas and variances and inverse variances. It gets challenging! One consideration is that you don't ever want to have infinities, so you want to use inverse variances (which become zero when data are missing). But on the other hand, you want to avoid singular or near-singular matrices (which happen when you have lots of vanishing inverse variances). So we settled on a consistent large value for sigma (and correspondingly small value for the inverse variance) that satisfies both issues for our problem.

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