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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

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Bensby, T. [1] ; Yee, J. C. [2] ; Feltzing, S. [1] ; Johnson, J. A. [2] ; Gould, A. [2] ; Cohen, J. G. [3] ; Asplund, M. [4] ; Melendez, J. [5] ; Lucatello, S. [6] ; Han, C. [7] ; Thompson, I. [8] ; Gal-Yam, A. [9] ; Udalski, A. [10] ; Bennett, D. P. [11] ; Bond, I. A. [12] ; Kohei, W. [13] ; Sumi, T. [13] ; Suzuki, D. [13] ; Suzuki, K. [14] ; Takino, S. [14] ; Tristram, P. [15] ; Yamai, N. [16] ; Yonehara, A. [16]
Número total de Autores: 23
Afiliação do(s) autor(es):
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[1] Lund Observ, Dept Astron & Theoret Phys, S-22100 Lund - Sweden
[2] Ohio State Univ, Dept Astron, Columbus, OH 43210 - USA
[3] CALTECH, Palomar Observ, Pasadena, CA 91125 - USA
[4] Mt Stromlo & Siding Spring Observ, Res Sch Astron & Astrophys, Weston, ACT 2611 - Australia
[5] Univ Sao Paulo, Dept Astron IAG USP, BR-05508900 Sao Paulo - Brazil
[6] Astron Observ Padova, INAF, I-35122 Padua - Italy
[7] Chungbuk Natl Univ, Dept Phys, Cheongju 361763 - South Korea
[8] Carnegie Observ, Pasadena, CA 91101 - USA
[9] Weizmann Inst Sci, Dept Particle Phys & Astrophys, IL-76100 Rehovot - Israel
[10] Univ Warsaw Observ, PL-00478 Warsaw - Poland
[11] Univ Notre Dame, Notre Dame, IN 46556 - USA
[12] Massey Univ, Inst Informat & Math Sci, Auckland 1330 - New Zealand
[13] Osaka Univ, Dept Earth & Space Sci, Osaka 5600043 - Japan
[14] Nagoya Univ, Solar Terr Environm Lab, Nagoya, Aichi 4648601 - Japan
[15] Mt John Observ, Lake Tekapo 8770 - New Zealand
[16] Kyoto Sangyo Univ, Fac Sci, Dept Phys, Kyoto 6038555 - Japan
Número total de Afiliações: 16
Tipo de documento: Artigo Científico
Fonte: Astronomy & Astrophysics; v. 549, JAN 2013.
Citações Web of Science: 231

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. (AU)

Processo FAPESP: 10/50930-6 - Evolução química e populações estelares galácticas e extragalácticas, por espectroscopia e imageamento
Beneficiário:Beatriz Leonor Silveira Barbuy
Linha de fomento: Auxílio à Pesquisa - Temático