At lunch, Young Wook Lee (Yonsei) gave a nice talk on the blue horizontal branch in Milky Way globular clusters, showing that its morphology and population is a very strong function of metallicity and, in particular, helium abundance. It appears that many of the Milky Way's most dense globular clusters have multiple populations with different helium abundances. This is hard to explain, but Lee hypothesizes that these may not be what we traditionally think of as globular clusters but rather the remnants of disrupted substructures accreted onto the Milky Way long ago.
Zolotov and I spent the afternoon planning her first paper and her dissertation, in preparation for her oral exam. Her first paper will focus on the kinematics of stars with different origins (formed in situ, accreted recently, accreted long ago) in a simulated Milky-Way-like galaxy.