Origins of the thick disk as traced by the alpha elements of metal-poor giant stars selected from RAVE

G. R. Ruchti, J. P. Fulbright, R. F G Wyse, G. F. Gilmore, O. Bienaymé, J. Binney, J. Bland-Hawthorn, R. Campbell, K. C. Freeman, B. K. Gibson, E. K. Grebel, A. Helmi, U. Munari, J. F. Navarro, Q. A. Parker, W. Reid, G. M. Seabroke, A. Siebert, A. Siviero, M. SteinmetzF. G. Watson, M. Williams, T. Zwitter

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46 Citations (Scopus)


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 Letter, we present abundances of four α-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 [α/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 [α/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 α-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.

Original languageEnglish
Pages (from-to)L92-L96
Number of pages5
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 1 Oct 2010

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