Issue |
A&A
Volume 549, January 2013
|
|
---|---|---|
Article Number | A147 | |
Number of page(s) | 26 | |
Section | Galactic structure, stellar clusters and populations | |
DOI | https://doi.org/10.1051/0004-6361/201220678 | |
Published online | 16 January 2013 |
Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars⋆,⋆⋆
V. Evidence for a wide age distribution and a complex MDF
1
Lund ObservatoryDepartment of Astronomy and Theoretical
physics, PO Box
43, 221 00
Lund, Sweden
e-mail: tbensby@astro.lu.se
2
Department of Astronomy, Ohio State University,
140 W. 18th Avenue,
Columbus, OH
43210,
USA
3
Palomar Observatory, Mail Stop 249-17, California Institute of
Technology, Pasadena,
CA
91125,
USA
4
Research School of Astronomy & Astrophysics, Mount Stromlo
Observatory, Cotter Road, Weston
Creek, 2611
ACT,
Australia
5
Departamento de Astronomia do IAG/USP, Universidade de São
Paulo, Rua do Matão
1226, 05508-900
São Paulo,
Brasil
6
INAF – Astronomical Observatory of Padova,
Vicolo dell’Osservatorio 5,
35122
Padova,
Italy
7
Department of Physics, Chungbuk National University,
361-763
Cheongju, Republic of
Korea
8
Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA
91101,
USA
9
Department of Particle Physics and Astrophysics, Weizmann
Institute of Science, 76100
Rehovot,
Israel
10
Warsaw University Observatory, A1. Ujazdowskie 4, 00-478, Warszawa, Poland
11
University of Notre Dame, Notre Dame, IN
46556,
USA
12
Institute for Information and Mathematical Sciences, Massey
University, 1330
Auckland, New
Zealand
13
Department of Earth and Space Science, Osaka
University, 560-0043
Osaka,
Japan
14
Solar-Terrestrial Environment Laboratory, Nagoya
University, 464-8601
Nagoya,
Japan
15
Mt. John Observatory, PO Box 56, 8770
Lake Tekapo, New
Zealand
16
Department of Physics, Faculty of Science, Kyoto Sangyo
University, 603-8555
Kyoto,
Japan
Received: 31 October 2012
Accepted: 28 November 2012
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.
Key words: gravitational lensing: micro / Galaxy: bulge / Galaxy: formation / Galaxy: evolution / stars: abundances
Based on data obtained with the European Southern Observatory telescopes (Proposal ID:s 87.B-0600, 88.B-0349, 89.B-0047, and 90.B-0204), the Magellan Clay telescope at the Las Campanas observatory, and the Keck I telescope at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration.
Tables 2–5 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A147
© ESO, 2013
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