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Chemical evolution of the galactic bulge as traced by microlensed dwarf and subgiant stars. II. Ages, metallicities, detailed elemental abundances, and connections to the Galactic thick disc

Bensby, Thomas LU ; Feltzing, Sofia LU ; Johnson, J.A.; Gould, A.; Adén, Daniel LU ; Asplund, M.; Melendez, J.; Gal-Yam, A.; Lucatello, S. and Sana, H., et al. (2010) In Astronomy & Astrophysics 512.
Abstract
Context. The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation and evolution of the Bulge comes from bright giant stars. The underlying assumption that giants represent all the stars, and accurately trace the chemical evolution of a stellar population, is under debate. In particular, recent observations of a few microlensed dwarf stars give a very different picture of the evolution of the Bulge from that given by the giant stars. Aims. We aim to resolve the apparent discrepancy between Bulge metallicity distributions derived from microlensed dwarf stars and giant stars. Additionally, we aim to put observational constraints on the elemental abundance trends and chemical... (More)
Context. The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation and evolution of the Bulge comes from bright giant stars. The underlying assumption that giants represent all the stars, and accurately trace the chemical evolution of a stellar population, is under debate. In particular, recent observations of a few microlensed dwarf stars give a very different picture of the evolution of the Bulge from that given by the giant stars. Aims. We aim to resolve the apparent discrepancy between Bulge metallicity distributions derived from microlensed dwarf stars and giant stars. Additionally, we aim to put observational constraints on the elemental abundance trends and chemical evolution of the Bulge. Methods. We perform a detailed elemental abundance analysis of dwarf stars in the Galactic bulge, based on high-resolution spectra that were obtained while the stars were optically magnified during gravitational microlensing events. The analysis method is the same as for a large sample of F and G dwarf stars in the Solar neighbourhood, enabling a fully differential comparison between the Bulge and the local stellar populations in the Galactic disc. Results. We present detailed elemental abundances and stellar ages for six new dwarf stars in the Galactic bulge. Combining these with previous events, here re-analysed with the same methods, we study a homogeneous sample of 15 stars, which constitute the largest sample to date of microlensed dwarf stars in the Galactic bulge. We find that the stars span the full range of metallicities from [Fe/H] = -0.72 to + 0.54, and an average metallicity of <[Fe/H]> = -0.08 +/- 0.47, close to the average metallicity based on giant stars in the Bulge. Furthermore, the stars follow well-defined abundance trends, that for [Fe/H]<0 are very similar to those of the local Galactic thick disc. This suggests that the Bulge and the thick disc have had, at least partially, comparable chemical histories. At sub-solar metallicities we find the Bulge dwarf stars to have consistently old ages, while at super-solar metallicities we find a wide range of ages. Using the new age and abundance results from the microlensed dwarf stars we investigate possible formation scenarios for the Bulge. (Less)
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publication status
published
subject
keywords
Galaxy: bulge, gravitational lensing: micro, Galaxy: formation, Galaxy:, evolution, Galaxy: disk, stars: abundances
in
Astronomy & Astrophysics
volume
512
publisher
EDP Sciences
external identifiers
  • wos:000276245500033
  • scopus:77951546489
ISSN
0004-6361
DOI
10.1051/0004-6361/200913744
language
English
LU publication?
yes
id
b2626599-2b81-4fa4-8c5a-efeca6409c23 (old id 1514745)
date added to LUP
2009-12-07 11:13:13
date last changed
2018-05-29 09:36:11
@article{b2626599-2b81-4fa4-8c5a-efeca6409c23,
  abstract     = {Context. The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation and evolution of the Bulge comes from bright giant stars. The underlying assumption that giants represent all the stars, and accurately trace the chemical evolution of a stellar population, is under debate. In particular, recent observations of a few microlensed dwarf stars give a very different picture of the evolution of the Bulge from that given by the giant stars. Aims. We aim to resolve the apparent discrepancy between Bulge metallicity distributions derived from microlensed dwarf stars and giant stars. Additionally, we aim to put observational constraints on the elemental abundance trends and chemical evolution of the Bulge. Methods. We perform a detailed elemental abundance analysis of dwarf stars in the Galactic bulge, based on high-resolution spectra that were obtained while the stars were optically magnified during gravitational microlensing events. The analysis method is the same as for a large sample of F and G dwarf stars in the Solar neighbourhood, enabling a fully differential comparison between the Bulge and the local stellar populations in the Galactic disc. Results. We present detailed elemental abundances and stellar ages for six new dwarf stars in the Galactic bulge. Combining these with previous events, here re-analysed with the same methods, we study a homogeneous sample of 15 stars, which constitute the largest sample to date of microlensed dwarf stars in the Galactic bulge. We find that the stars span the full range of metallicities from [Fe/H] = -0.72 to + 0.54, and an average metallicity of &lt;[Fe/H]&gt; = -0.08 +/- 0.47, close to the average metallicity based on giant stars in the Bulge. Furthermore, the stars follow well-defined abundance trends, that for [Fe/H]&lt;0 are very similar to those of the local Galactic thick disc. This suggests that the Bulge and the thick disc have had, at least partially, comparable chemical histories. At sub-solar metallicities we find the Bulge dwarf stars to have consistently old ages, while at super-solar metallicities we find a wide range of ages. Using the new age and abundance results from the microlensed dwarf stars we investigate possible formation scenarios for the Bulge.},
  articleno    = {A41},
  author       = {Bensby, Thomas and Feltzing, Sofia and Johnson, J.A. and Gould, A. and Adén, Daniel and Asplund, M. and Melendez, J. and Gal-Yam, A. and Lucatello, S. and Sana, H. and Sumi, T. and Miyake, N. and Suzuki, D. and Han, C. and Bond, I. and Udalski, A.},
  issn         = {0004-6361},
  keyword      = {Galaxy: bulge,gravitational lensing: micro,Galaxy: formation,Galaxy:,evolution,Galaxy: disk,stars: abundances},
  language     = {eng},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {Chemical evolution of the galactic bulge as traced by microlensed dwarf and subgiant stars. II. Ages, metallicities, detailed elemental abundances, and connections to the Galactic thick disc},
  url          = {http://dx.doi.org/10.1051/0004-6361/200913744},
  volume       = {512},
  year         = {2010},
}