Today started my summer at MPIA in Heidelberg. I had many conversations with Hans-Walter Rix about our various projects, and then spent a long time working with Melissa Ness on pairs of stars with near-identical abundances. Ness finds that if the stars are very, very close in 19-dimensional abundance space, they also tend to be close in position (like within 500 pc). That's hard to understand, since red-clump stars (her targets) are a few Gyr old, and in a few Gyr, two stars that are formed together ought to have drifted apart by a few kpc!
Her results are surprising if true. This left us at the end of the day with Ness working to see if there are any issues with the data that could be causing the problems, and Rix and I discussing possible astrophysical explanations. Julianne Dalcanton (UW) and Rix jointly suggested that we are finding disrupted binaries, that are disrupting because of the red-giant mass loss that leads to red-clumpiness! This explanation is insane but works on many levels. Now to test it.