The age of the Milky Way halo stars from the Sloan Digital Sky Survey
Paula Jofre, Achim Weiss (Max-Planck-Institut fuer Astrophysik)

TL;DR
This study used Sloan Digital Sky Survey data to determine the age of Milky Way halo stars, finding a rapid formation of the dominant population and providing insights into stellar evolution processes.
Contribution
It presents a new method to estimate halo star ages using turn-off temperatures across metallicities, and compares models with and without atomic diffusion.
Findings
No age gradient with metallicity, indicating rapid formation
Ages of 14-16 Gyr without diffusion, conflicting with the Universe's age
Ages of 10-12 Gyr with diffusion, aligning with globular cluster ages
Abstract
We determined the age of the stellar content of the Galactic halo by considering main-sequence turn-off stars. From the large number of halo stars provided by Sloan Digital Sky Survey, we could accurately detect the turn-off as a function of metallicity of the youngest dominant population, which was done by looking at the hottest (bluest) stars of a population. Using the turn-off temperature of a population of a given metallicity, we looked for the isochrones with that turn-off temperature and metallicity and found no age gradient as a function of metallicity. This would mean that this dominating population of the Galactic halo formed rapidly, probably during the collapse of the proto-Galactic gas. Moreover, we could find a significant number of stars with hotter temperatures than the turn-off, which might be blue horizontal branch (BHB) stars, blue stragglers, or main sequence stars…
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