I spent part of the weekend looking at issues with chemical abundances as a function of position and velocity in the Solar neighborhood. In the data, it looks like somehow the main-sequence abundances in the APOGEE and GALAH data sets are different for stars in different positions along the same orbit. That's bad for my Chemical Torus Imaging (tm) project with Adrian Price-Whelan (Flatiron)! But slowly we realized that the issue is that the abundances depend on stellar effective temperatures, and different temperatures are differently represented in different parts of the orbit. Phew. But there is a problem with the data. (Okay actually this can be a real, physical effect or a problem with the data; either way, we have to deal.) Time to call Christina Eilers (MIT), who is thinking about exactly this kind of abundance-calibration problem.
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