Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 721, Issue 2, Pages L92-L96Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/721/2/L92
Keywords
Galaxy: abundances; Galaxy: disk; stars: abundances; stars: late-type
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Funding
- W. M. Keck Foundation
- Gordon and Betty Moore Foundation
- NSF [AST-0908326]
- NASA
- Science and Technology Facilities Council [ST/G002509/1, PP/D001242/1, ST/H00243X/1, ST/F002432/1, ST/G002479/1, PP/D001528/1] Funding Source: researchfish
- UK Space Agency [PP/D006570/1] Funding Source: researchfish
- STFC [ST/G002509/1, PP/D001242/1, ST/G002479/1, ST/F002432/1, PP/D001528/1] Funding Source: UKRI
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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] less than or similar to -1.0) and to measure their elemental abundances. In this Letter, we present abundances of four alpha-elements (Mg, Si, Ca, and Ti) and iron for a subsample of 212 red giant branch and 31 red clump/horizontal branch 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 interstellar medium 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 initial mass function. 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.
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