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The Galactic Disk-Halo Transition – Evidence from Stellar Abundances†

Published online by Cambridge University Press:  01 June 2008

Poul Erik Nissen  and
William J. Schuster
Poul Erik Nissen
Affiliation:
Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark email: pen@phys.au.dk
William J. Schuster
Affiliation:
Observatorio Astronómico Nacional, Universidad Nacional Autónoma de México, Apartado Postal 877, Ensenada, BC, 22800México email: schuster@astrosen.unam.mx
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Abstract

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New information on the relations between the Galactic disks, the halo, and satellite galaxies is being obtained from elemental abundances of stars having metallicities in the range −1.5 < [Fe/H] < −0.5. The first results for a sample of 26 halo stars and 13 thick-disk stars observed with the ESO VLT/UVES spectrograph are presented. The halo stars fall in two distinct groups: one group (9 stars) has [α/Fe] = 0.30 ± 0.03 like the thick-disk stars. The other group (17 stars) shows a clearly deviating trend ranging from [α/Fe] = 0.20 at [Fe/H] = −1.3 to [α/Fe] = 0.08 at [Fe/H] = −0.8. The kinematics of the stars are discussed and the abundance ratios Na/Fe, Ni/Fe, Cu/Fe and Ba/Y are applied to see if the “low-alpha” stars are connected to the thin disk or to Milky Way satellite galaxies. Furthermore, we compare our data with simulations of chemical abundance distributions in hierarchically formed stellar halos in a ΛCDM Universe.

Keywords

stars: abundancesGalaxy: diskGalaxy: haloGalaxy: evolution
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Issue S254: The Galaxy Disk in Cosmological Context , June 2008 , pp. 103 - 108
Copyright
Copyright © International Astronomical Union 2009

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