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arXiv · 1008.3828

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. Steinmetz·F. G. Watson·M. Williams·T. Zwitter
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Abstract

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.

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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. Steinmetz, F. G. Watson, M. Williams, T. Zwitter. 2010-08-23. Origins of the Thick Disk as Traced by the Alpha-Elements of Metal-Poor Giant Stars Selected from RAVE. https://doi.org/10.1088/2041-8205%2F721%2F2%2Fl92

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