Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2010-08-23
Astrophysical Journal Letters 721 (2010) L92-L96
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
11 pages, 2 figures, accepted by ApJ Letters
Scientific paper
Theories of thick disk formation can be differentiated by measurements of stellar elemental abundances. We have undertaken a study of metal-poor stars selected from the RAVE spectroscopic survey of bright stars to establish whether or not there is a significant population of metal-poor thick-disk stars ([Fe/H] <~ -1.0) and to measure their elemental abundances. In this paper, we present abundances of four alpha-elements (Mg, Si, Ca, Ti) and iron for a subsample of 212 RGB and 31 RC/HB stars from this study. We find that the [alpha/Fe] ratios are enhanced implying that enrichment proceeded by purely core-collapse supernovae. This requires that star formation in each star forming region had a short duration. The relative lack of scatter in the [alpha/Fe] ratios implies good mixing in the ISM prior to star formation. In addition, the ratios resemble that of the halo, indicating that the halo and thick disk share a similar massive star IMF. We conclude that the alpha enhancement of the metal-poor thick disk implies that direct accretion of stars from dwarf galaxies similar to surviving dwarf galaxies today did not play a major role in the formation of the thick disk.
Bienayme Olivier
Binney James
Bland-Hawthorn Jonathan
Campbell Randy
Freeman Ken C.
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