2009A&A...499..737B


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.04CEST19:56:54

2009A&A...499..737B - Astronomy and Astrophysics, volume 499, 737-753 (2009/6-1)

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. Detailed abundance analysis of OGLE-2008-BLG-209S.

BENSBY T., JOHNSON J.A., COHEN J., FELTZING S., UDALSKI A., GOULD A., HUANG W., THOMPSON I., SIMMERER J. and ADEN D.

Abstract (from CDS):

Our aims are twofold. First we aim to evaluate the robustness and accuracy of stellar parameters and detailed elemental abundances that can be derived from high-resolution spectroscopic observations of microlensed dwarf and subgiant stars. We then aim to use microlensed dwarf and subgiant stars to investigate the abundance structure and chemical evolution of the Milky Way Bulge. Contrary to the cool giant stars, with their extremely crowded spectra, the dwarf stars are hotter, their spectra are cleaner, and the elemental abundances of the atmospheres of dwarf and subgiant stars are largely untouched by the internal nuclear processes of the star. We present a detailed elemental abundance analysis of OGLE-2008-BLG-209S, the source star of a new microlensing event towards the Bulge, for which we obtained a high-resolution spectrum with the MIKE spectrograph on the Magellan Clay telescope. We have performed four different analyses of OGLE-2008-BLG-209S. One method is identical to the one used for a large comparison sample of F and G dwarf stars, mainly thin and thick disc stars, in the Solar neighbourhood. We have also re-analysed three previous microlensed dwarf stars OGLE-2006-BLG-265S, MOA-2006-BLG-099S, and OGLE-2007-BLG-349S with the same method. This homogeneous data set, although small, enables a direct comparison between the different stellar populations. We find that OGLE-2008-BLG-209S is a subgiant star that has a metallicity of [Fe/H]≃-0.33. It possesses [α/Fe] enhancements similar to what is found for Bulge giant stars at the same metallicity, and what also is found for nearby thick disc stars at the same metallicity. In contrast, the previous three microlensing dwarf stars have very high metallicities, [Fe/H]>+0.4, and more solar-like abundance ratios, i.e. [α/Fe]≃0. The decrease in the [α/Fe] ratio with [Fe/H] is the typical signature of enrichment from low and intermediate mass stars. We furthermore find that the results for the four Bulge stars, in combination with results from studies of giant stars in the Bulge, seem to favour a secular formation scenario for the Bulge.

Abstract Copyright:

Journal keyword(s): gravitational lensing - Galaxy: bulge - Galaxy: formation - Galaxy: evolution - stars: fundamental parameters - stars: abundances

VizieR on-line data: <Available at CDS (J/A+A/499/737): table2.dat>

Simbad objects: 11

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Number of rows : 11

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME Gal Center reg 17 45 40.04 -29 00 28.1           ~ 11533 0
2 MOA 2006-BUL-99 * 17 54 10.99 -35 13 38.0           G 11 0
3 MOA 2008-BLG-310 * 17 54 14.53 -34 46 41.0           GV 40 1
4 MOA 2008-BLG-311 * 17 56 53.65 -31 23 49.9           ~ 13 0
5 EWS 2007-BUL-514 * 17 58 03.09 -27 31 05.7           ~ 12 0
6 NAME Baade Window reg 18 03.5 -30 01           ~ 528 3
7 EWS 2008-BUL-209 * 18 04 49.84 -29 42 33.2           ~ 11 0
8 MOA 2007-BLG-379 ** 18 05 24.43 -26 25 18.8           ~ 31 1
9 EWS 2006-BUL-265 * 18 07 18.88 -27 47 42.7           G 14 0
10 MACHO 97-BLG-45 Lev 18 21 01.80 -28 46 45.0     19.8     ~ 11 0
11 NAME Galactic Bulge reg ~ ~           ~ 3387 0

    Equat.    Gal    SGal    Ecl

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2020.07.04-19:56:54

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