ORIGINS OF THE THICK DISK AS TRACED BY THE ALPHA ELEMENTS OF METAL-POOR GIANT STARS SELECTED FROM RAVE

Journal Article · Fri Oct 01 04:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/721/2/L92· OSTI ID:21452793

Ruchti, G R; Fulbright, J P; Wyse, R F. G. ^[1]; Gilmore, G F ^[2]; Bienayme, O; Siebert, A ^[3]; Binney, J ^[4]; Bland-Hawthorn, J ^[5]; Campbell, R ^[6]; Freeman, K C ^[7]; Gibson, B K ^[8]; Grebel, E K ^[9]; Helmi, A ^[10]; Munari, U ^[11]; Navarro, J F; Siviero, A ^[12]; Parker, Q A; Reid, W ^[13]; Seabroke, G M ^[14]; Steinmetz, M ^[15]

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1. Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
2. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
3. Observatoire de Strasbourg, 11 Rue de L'Universite, 67000 Strasbourg (France)
4. Rudolf Pierls Center for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP (United Kingdom)
5. Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006 (Australia)
6. Western Kentucky University, 1906 College Heights Blvd., Bowling Green, KY 42101 (United States)
7. RSAA Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, Canberra, ACT 2611 (Australia)
8. Jeremiah Horrocks Institute for Astrophysics and Super-computing, University of Central Lancashire, Preston (United Kingdom)
9. Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg, D-69120 Heidelberg (Germany)
10. Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands)
11. INAF Osservatorio Astronomico di Padova, Via dell'Osservatorio 8, Asiago I-36012 (Italy)
12. University of Victoria, P.O. Box 3055, Station CSC, Victoria, BC V8W 3P6 (Canada)
13. Macquarie University, Sydney, NSW 2109 (Australia)
14. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom)
15. 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, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 721; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
BINARY STARS
ERUPTIVE VARIABLE STARS
GALAXIES
GIANT STARS
MASS
STARS
SUPERNOVAE
VARIABLE STARS