TY - JOUR
T1 - Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars
T2 - V. Evidence for a wide age distribution and a complex MDF
AU - Bensby, T.
AU - Yee, J. C.
AU - Feltzing, S.
AU - Johnson, J. A.
AU - Gould, A.
AU - Cohen, J. G.
AU - Asplund, M.
AU - Melendez, J.
AU - Lucatello, S.
AU - Han, C.
AU - Thompson, I.
AU - Gal-Yam, Avishay
AU - Udalski, A.
AU - Bennett, D. P.
AU - Bond, I. A.
AU - Kohei, W.
AU - Sumi, T.
AU - Suzuki, D.
AU - Suzuki, K.
N1 - Swedish Research Council [621-2009-3911, 2008-4095]; SNSF Graduate Research Fellowsh [2009068160]; NSF [AST-1103471, 1066293, AST-0908139]; Australian Research Council [FL110100012]; INAF PRIN grant "Multiple populations in Globular Clusters: their role in the Galaxy assembly"; FAPESP [2010/50930-6]; USP (Novos Docentes); CNPq (Bolsa de produtividade); Lord Sieff of Brimpton Fund; European Research Council under the European Community's Seventh Framework Programme (FP7) / ERC [246678]; Creative Research Initiative Program of National Research Foundation of Korea [2009-0081561]We are grateful to and thank Patrick Baumann who obtained the MIKE spectrum for MOA-2011-BLG-234S, Julio Chaname who obtained the MIKE spectrum for MOA-2011-BLG-278S, G.W. Marcy who obtained the HIRES spectra for MOA-2011-BLG-191S and OGLE-2012-BLG-0816S, and Elizabeth Wylie and Mario Mateo who obtained the MIKE spectrum for OGLE-2012-BLG-1279S. We would also like to thank Bengt Gustafsson, Bengt Edvardsson, and Kjell Eriksson for usage of the MARCS model atmosphere program and their suite of stellar abundance programs. T.B. was funded by grant No. 621-2009-3911 from The Swedish Research Council. S.F. was partly funded by grant No. 2008-4095 from The Swedish Research Council. Work by J.C.Y. was supported by an SNSF Graduate Research Fellowship under Grant No. 2009068160. A.G. and J.C.Y. acknowledge support from NSF AST-1103471. M.A. gratefully acknowledges funding from the Australian Research Council (FL110100012). J.L.C. is grateful to NSF award AST-0908139 for partial support. S.L. reasearch is partially supported by the INAF PRIN grant "Multiple populations in Globular Clusters: their role in the Galaxy assembly" J.M. thanks support from FAPESP (2010/50930-6), USP (Novos Docentes) and CNPq (Bolsa de produtividade). A.G.-Y. acknowledges support by the Lord Sieff of Brimpton Fund. The OGLE project has received funding from the European Research Council under the European Community's Seve
PY - 2013
Y1 - 2013
N2 - Based on high-resolution spectra obtained during gravitational microlensing events we present a detailed elemental abundance analysis of 32 dwarf and subgiant stars in the Galactic bulge. Combined with the sample of 26 stars from the previous papers in this series, we now have 58 microlensed bulge dwarfs and subgiants that have been homogeneously analysed. The main characteristics of the sample and the findings that can be drawn are: (i) the metallicity distribution (MDF) is wide and spans all metallicities between [Fe/H] = -1.9 to +0.6; (ii) the dip in the MDF around solar metallicity that was apparent in our previous analysis of a smaller sample (26 microlensed stars) is no longer evident; instead it has a complex structure and indications of multiple components are starting to emerge. A tentative interpretation is that there could be different stellar populations at interplay, each with a different scale height: the thin disk, the thick disk, and a bar population; (iii) the stars with [Fe/H] ≤ -0.1 are old with ages between 10 and 12 Gyr; (iv) the metal-rich stars with [Fe/H] ≥ -0.1 show a wide variety of ages, ranging from 2 to 12 Gyr with a distribution that has a dominant peak around 4-5 Gyr and a tail towards higher ages; (v) there are indications in the [α/Fe]-[Fe/H] abundance trends that the "knee" occurs around [Fe/H] = -0.3to -0.2, which is a slightly higher metallicity as compared to the "knee" for the local thick disk. This suggests that the chemical enrichment of the metal-poor bulge has been somewhat faster than what is observed for the local thick disk. The results from the microlensed bulge dwarf stars in combination with other findings in the literature, in particular the evidence that the bulge has cylindrical rotation, indicate that the Milky Way could be an almost pure disk galaxy. The bulge would then just be a conglomerate of the other Galactic stellar populations (thin disk, thick disk, halo, and.?), residing together in the central parts of the Galaxy, influenced by the Galactic bar.
AB - Based on high-resolution spectra obtained during gravitational microlensing events we present a detailed elemental abundance analysis of 32 dwarf and subgiant stars in the Galactic bulge. Combined with the sample of 26 stars from the previous papers in this series, we now have 58 microlensed bulge dwarfs and subgiants that have been homogeneously analysed. The main characteristics of the sample and the findings that can be drawn are: (i) the metallicity distribution (MDF) is wide and spans all metallicities between [Fe/H] = -1.9 to +0.6; (ii) the dip in the MDF around solar metallicity that was apparent in our previous analysis of a smaller sample (26 microlensed stars) is no longer evident; instead it has a complex structure and indications of multiple components are starting to emerge. A tentative interpretation is that there could be different stellar populations at interplay, each with a different scale height: the thin disk, the thick disk, and a bar population; (iii) the stars with [Fe/H] ≤ -0.1 are old with ages between 10 and 12 Gyr; (iv) the metal-rich stars with [Fe/H] ≥ -0.1 show a wide variety of ages, ranging from 2 to 12 Gyr with a distribution that has a dominant peak around 4-5 Gyr and a tail towards higher ages; (v) there are indications in the [α/Fe]-[Fe/H] abundance trends that the "knee" occurs around [Fe/H] = -0.3to -0.2, which is a slightly higher metallicity as compared to the "knee" for the local thick disk. This suggests that the chemical enrichment of the metal-poor bulge has been somewhat faster than what is observed for the local thick disk. The results from the microlensed bulge dwarf stars in combination with other findings in the literature, in particular the evidence that the bulge has cylindrical rotation, indicate that the Milky Way could be an almost pure disk galaxy. The bulge would then just be a conglomerate of the other Galactic stellar populations (thin disk, thick disk, halo, and.?), residing together in the central parts of the Galaxy, influenced by the Galactic bar.
UR - http://www.scopus.com/inward/record.url?scp=84872578931&partnerID=8YFLogxK
U2 - https://doi.org/10.1051/0004-6361/201220678
DO - https://doi.org/10.1051/0004-6361/201220678
M3 - مقالة
SN - 0004-6361
VL - 549
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
M1 - A147
ER -