Today Christina Eilers (MIT) and I looked at plots she made of element abundances in red-giant-branch stars as measured in the APOGEE data. She plotted abundances as a function of position in the Galaxy and surface gravity. Our expectation is that the abundance distribution should be a strong function of galactocentric radius and height above the disk plane, but a very weak (or null) function of stellar surface gravity: After all, stars at different surface gravities (and we are only looking at the stars above the red clump) are just at marginally different evolutionary stages; they shouldn't (on average) be very different in age or formation. This is a baby step towards building an empirical model of element-abundance measurement systematics, to self-calibrate a better set of abundances. We discussed details of visualization and communication of the results, for presentation to the APOGEE team for discussion.
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