We can now map the stars in the Milky Way on truly galactic scales, thanks to recent surveys that are reaching across the disk, such as APOGEE, GALAH, K2 and Gaia. I will first discuss the new insights we have into the ages of stars throughout the disk derived from chemical ages and verified through fundamental measurements from Kepler, K2, and Gaia. The APOGEE survey has also shown that the distribution of alpha-rich and metal-rich stars varies across the disk. However, these variations are not accompanied by strong changes in the elemental abundance ratios. This both limits the amount that the initial mass function, for example, has changed over the disk and provides a way to empirically determine the contributions from core-collapse supernovae vs. Type 1a supernovae. GALAH has measured additional elements, and we have subjected them to a similar analysis. I discuss the confirmations and surprises of confronting these observations with predicitons from theory.
Speaker: Jennifer Johnson, Ohio State Univ.
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