As my loyal reader knows, Christina Eilers (MIT) and I have been looking at surface-gravity systematics in surface-abundance measurements in red-giant stars. It appears that stars with different gravities say different things about the abundance trends with (say) Galactocentric radius and perpendicular distance from the midplane. And none of these things agrees with the trends published in the literature by various groups. We now think that the published trends are caused by selection differences as a function of Galactic azimuth (probably primarily beause of crowding), plus these surface-gravity effects. Today we discussed with Hans-Walter Rix (MPIA) the scope of such projects, and we were able to establish a limited scope that we think will work. But one step on the path is to argue all this out with the APOGEE team, because we need to understand whether our interpretations of all these things are correct.
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