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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

Bensby, Thomas LU orcid ; Yee, J. C. ; Feltzing, Sofia LU orcid ; Johnson, J. A. ; Gould, A. ; Cohen, J. G. ; Asplund, M. ; Melendez, J. ; Lucatello, S. and Han, C. , et al. (2013) In Astronomy & Astrophysics 549.
Abstract
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... (More)
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] less than or similar to -0.1 are old with ages between 10 and 12 Gyr; (iv) the metal-rich stars with [Fe/H] greater than or similar to -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 [alpha/Fe] - [Fe/H] abundance trends that the "knee" occurs around [Fe/H] = -0.3 to -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. (Less)
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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
gravitational lensing: micro, Galaxy: bulge, Galaxy: formation, Galaxy:, evolution, stars: abundances
in
Astronomy & Astrophysics
volume
549
article number
A147
publisher
EDP Sciences
external identifiers
  • wos:000313745000147
  • scopus:84872578931
ISSN
0004-6361
DOI
10.1051/0004-6361/201220678
language
English
LU publication?
yes
id
d5be5d60-aae4-4a31-a65b-1f59d3607a02 (old id 3595955)
date added to LUP
2016-04-01 13:53:01
date last changed
2024-04-10 11:50:48
@article{d5be5d60-aae4-4a31-a65b-1f59d3607a02,
  abstract     = {{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] less than or similar to -0.1 are old with ages between 10 and 12 Gyr; (iv) the metal-rich stars with [Fe/H] greater than or similar to -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 [alpha/Fe] - [Fe/H] abundance trends that the "knee" occurs around [Fe/H] = -0.3 to -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.}},
  author       = {{Bensby, Thomas and Yee, J. C. and Feltzing, Sofia and Johnson, J. A. and Gould, A. and Cohen, J. G. and Asplund, M. and Melendez, J. and Lucatello, S. and Han, C. and Thompson, I. and Gal-Yam, A. and Udalski, A. and Bennett, D. P. and Bond, I. A. and Kohei, W. and Sumi, T. and Suzuki, D. and Suzuki, K. and Takino, S. and Tristram, P. and Yamai, N. and Yonehara, A.}},
  issn         = {{0004-6361}},
  keywords     = {{gravitational lensing: micro; Galaxy: bulge; Galaxy: formation; Galaxy:; evolution; 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 V. Evidence for a wide age distribution and a complex MDF}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/201220678}},
  doi          = {{10.1051/0004-6361/201220678}},
  volume       = {{549}},
  year         = {{2013}},
}