Seminar: Young stars in the Galactic bulge? A mystery explored using modern isochrones, careful statistics, and model uncertainties

In 2017, Benbsy et al. presented ages for a sample of 91 subdwarf stars in the Galactic bulge. Their physical parameters (surface gravities, effective temperatures, and metallicities) were determined spectroscopically and independently of distance thanks to the magnification of microlensing events. The Bensby et al., (2017) analysis finds a large constituency of young stars (<= 2.5 Gyr) in the bulge: a prominent result that has called into question our understanding of the formation history of the Galaxy. However, a re-determination of these stellar ages using Bensby et al.’s own measurements tells a different story. Using modern isochrones from the MIST (MESA Isochrones and Stellar Tracks) database and carefully applied statistical techniques, an age distribution notably lacking in very young stars is revealed.

In this talk, I will argue that the "fundamental tension" between the spectroscopically derived age distribution for this Galactic Bulge population and photometric determination of the same region may in fact be reconciled through appropriate treatment of model uncertainties in the 1D stellar evolution codes used to derive fundamental parameters. I use the 1D convective mixing length parameter, alpha_MLT, as a demonstration.

Time permitting, I will also demonstrate the impact of similar considerations in models of Betelgeuse.

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We will go to lunch at 12:20. There will be fika in the astronomy corridor (Hus 9 Plan 5) after the seminar.