Age-Dating Red Giant Stars Associated with Galactic Disk and Halo Substructures

Understand

The vast majority of Milky Way stellar halo stars were likely accreted from a small number ($\lesssim$3) of relatively large dwarf galaxy accretion events.

• However, the timing of these events is poorly constrained, relying predominantly on indirect dynamical mixing arguments or imprecise age measurements of stars associated with debris structures.
• Here, we aim to infer robust stellar ages for stars associated with galactic substructures to more directly constrain the merger history of the Galaxy.
• By combining kinematic, asteroseismic, and spectroscopic data where available, we infer stellar ages for a sample of 10 red giant stars that were kinematically selected to be associated with the stellar halo, a subset of which are associated with the Gaia-Enceladus-Sausage halo substructure, and compare their ages to 3 red giant stars in the Galactic disk.