The age of the Milky Way halo stars from the Sloan Digital Sky Survey

P. Jofre 1 Achim Weiss 2
1 M2A 2011
L3AB - Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux, OASU - Observatoire aquitain des sciences de l'univers, LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac], Université Sciences et Technologies - Bordeaux 1
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 that are younger than the dominant population and were probably formed in external galaxies and accreted later on to our Milky Way. Motivated by the current debate about the efficiency of gravitational settling (atomic diffusion) in the interior of old solar-type stars, we used isochrones with and without settling to determine the ages. When ignoring diffusion in the isochrones we obtained ages of 14-16 Gyr. This result is a strong argument against inhibited diffusion in old halo field stars, since it results in a serious conflict with the age of the Universe of 13.7 Gyr. The age obtained including diffusion in the isochrones was 10-12 Gyr, which agrees with the absolute age of the old globular clusters in the inner halo.
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https://hal.archives-ouvertes.fr/hal-00670015
Contributeur : Marie-Paule Pomies <>
Soumis le : mardi 14 février 2012 - 12:51:35
Dernière modification le : mercredi 19 septembre 2018 - 01:27:18

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P. Jofre, Achim Weiss. The age of the Milky Way halo stars from the Sloan Digital Sky Survey. Astronomy and Astrophysics - A&A, EDP Sciences, 2011, 533, pp.A59. 〈10.1051/0004-6361/201117131〉. 〈hal-00670015〉

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