ORIGINS OF THE THICK DISK AS TRACED BY THE ALPHA ELEMENTS OF METAL-POOR GIANT STARS SELECTED FROM RAVE
- Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Observatoire de Strasbourg, 11 Rue de L'Universite, 67000 Strasbourg (France)
- Rudolf Pierls Center for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP (United Kingdom)
- Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006 (Australia)
- Western Kentucky University, 1906 College Heights Blvd., Bowling Green, KY 42101 (United States)
- RSAA Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, Canberra, ACT 2611 (Australia)
- Jeremiah Horrocks Institute for Astrophysics and Super-computing, University of Central Lancashire, Preston (United Kingdom)
- Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg, D-69120 Heidelberg (Germany)
- Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands)
- INAF Osservatorio Astronomico di Padova, Via dell'Osservatorio 8, Asiago I-36012 (Italy)
- University of Victoria, P.O. Box 3055, Station CSC, Victoria, BC V8W 3P6 (Canada)
- Macquarie University, Sydney, NSW 2109 (Australia)
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom)
- Astrophysikalisches Institut Potsdam, An der Sterwarte 16, D-14482 Potsdam (Germany)
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] {approx_lt} -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.
- OSTI ID:
- 21452793
- Journal Information:
- Astrophysical Journal Letters, Vol. 721, Issue 2; Other Information: DOI: 10.1088/2041-8205/721/2/L92; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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