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OGLE-2009-BLG-076S: THE MOST METAL-POOR DWARF STAR IN THE GALACTIC BULGE

Bensby, Thomas LU ; Feltzing, Sofia LU ; Johnson, J. A.; Gal-Yam, A.; Udalski, A.; Gould, A.; Han, C.; Adén, Daniel LU and Simmerer, Jennifer LU (2009) In Astrophysical Journal 699(2). p.174-177
Abstract
Measurements based on a large number of red giant stars suggest a broad metallicity distribution function (MDF) for the Galactic bulge, centered on [Fe/H] approximate to -0.1. However, recently, a new opportunity emerged to utilize temporary flux amplification (by factors of similar to 100 or more) of faint dwarf stars in the Bulge which are gravitationally lensed, making them observable with high-resolution spectrographs during a short observational window. Surprisingly, of the first six stars measured, five have [Fe/H] > +0.30, suggesting a highly skewed MDF, inconsistent with observations of giant stars. Here we present a detailed elemental abundance analysis of OGLE-2009-BLG-076S, based on a high-resolution spectrum obtained with... (More)
Measurements based on a large number of red giant stars suggest a broad metallicity distribution function (MDF) for the Galactic bulge, centered on [Fe/H] approximate to -0.1. However, recently, a new opportunity emerged to utilize temporary flux amplification (by factors of similar to 100 or more) of faint dwarf stars in the Bulge which are gravitationally lensed, making them observable with high-resolution spectrographs during a short observational window. Surprisingly, of the first six stars measured, five have [Fe/H] > +0.30, suggesting a highly skewed MDF, inconsistent with observations of giant stars. Here we present a detailed elemental abundance analysis of OGLE-2009-BLG-076S, based on a high-resolution spectrum obtained with the UVES spectrograph at the ESO Very Large Telescope. Our results indicate it is the most metal-poor dwarf star in the Bulge yet observed, with [Fe/H] = -0.76. Our results argue against a strong selection effect disfavoring metal-poor microlensed stars. It is possible that small number statistics is responsible for the giant/dwarf Bulge MDF discrepancy. Should this discrepancy survive when larger numbers of Bulge dwarf stars (soon to be available) are analyzed, it may require modification of our understanding of either Bulge formation models, or the behavior of metal-rich giant stars. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
stars: abundances, lensing, stars: fundamental parameters, gravitational, Galaxy: formation, Galaxy: evolution, Galaxy: bulge
in
Astrophysical Journal
volume
699
issue
2
pages
174 - 177
publisher
University of Chicago Press
external identifiers
  • wos:000267372800026
  • scopus:77950632108
ISSN
0004-637X
DOI
10.1088/0004-637X/699/2/L174
language
English
LU publication?
yes
id
8408f3d8-b5ce-4345-b980-7cad65197958 (old id 1441518)
date added to LUP
2009-07-28 08:58:11
date last changed
2017-01-01 05:22:00
@article{8408f3d8-b5ce-4345-b980-7cad65197958,
  abstract     = {Measurements based on a large number of red giant stars suggest a broad metallicity distribution function (MDF) for the Galactic bulge, centered on [Fe/H] approximate to -0.1. However, recently, a new opportunity emerged to utilize temporary flux amplification (by factors of similar to 100 or more) of faint dwarf stars in the Bulge which are gravitationally lensed, making them observable with high-resolution spectrographs during a short observational window. Surprisingly, of the first six stars measured, five have [Fe/H] > +0.30, suggesting a highly skewed MDF, inconsistent with observations of giant stars. Here we present a detailed elemental abundance analysis of OGLE-2009-BLG-076S, based on a high-resolution spectrum obtained with the UVES spectrograph at the ESO Very Large Telescope. Our results indicate it is the most metal-poor dwarf star in the Bulge yet observed, with [Fe/H] = -0.76. Our results argue against a strong selection effect disfavoring metal-poor microlensed stars. It is possible that small number statistics is responsible for the giant/dwarf Bulge MDF discrepancy. Should this discrepancy survive when larger numbers of Bulge dwarf stars (soon to be available) are analyzed, it may require modification of our understanding of either Bulge formation models, or the behavior of metal-rich giant stars.},
  author       = {Bensby, Thomas and Feltzing, Sofia and Johnson, J. A. and Gal-Yam, A. and Udalski, A. and Gould, A. and Han, C. and Adén, Daniel and Simmerer, Jennifer},
  issn         = {0004-637X},
  keyword      = {stars: abundances,lensing,stars: fundamental parameters,gravitational,Galaxy: formation,Galaxy: evolution,Galaxy: bulge},
  language     = {eng},
  number       = {2},
  pages        = {174--177},
  publisher    = {University of Chicago Press},
  series       = {Astrophysical Journal},
  title        = {OGLE-2009-BLG-076S: THE MOST METAL-POOR DWARF STAR IN THE GALACTIC BULGE},
  url          = {http://dx.doi.org/10.1088/0004-637X/699/2/L174},
  volume       = {699},
  year         = {2009},
}