Dartmouth Events

Physics and Astronomy - Astronomy Seminar - Meridith Joyce, STScI

Title: "Young stars in the Galactic bulge? Revised age determinations of micro-lensed subdwarfs with modern isochrones and statistical techniques"

Thursday, March 31, 2022
3:00pm – 4:00pm
Wilder 115
Intended Audience(s): Public
Categories: Lectures & Seminars

Abstract: In 2017, Benbsy et al. presented ages for a sample of 91 subdwarf stars in the Galactic bulge whose physical parameters (surface gravities, effective temperatures, and metallicities) were determined independently of photometric system and without reliance on distance thanks to the unique circumstances of microlensing events. Their analysis finds a large constituency of young stars (<= 2.5 Gyr) in the bulge: a prominent result that has called into question astronomers' 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, carefully applied statistical techniques, and taking into account the effects of alpha-element enhancement in metallicity, we find an age distribution notably lacking in very young stars. While our age distribution does include a tail consisting of some young stars, we do not reproduce the overabundance at 4 Gyr reported by Bensby et al., 2017. Further, we find a mean age for this population about 2-3 Gyr higher than the mean age reported in the initial study. In this seminar, I will discuss the age determination techniques used in this study, emphasizing in particular the role of uncertainties, and the implications our age distribution carries for Galactic formation scenarios.

For more information, contact:
Tressena Manning

Events are free and open to the public unless otherwise noted.