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Thomas Bensby. Profile photo.

Thomas Bensby

Senior lecturer

Thomas Bensby. Profile photo.

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

Author

  • Thomas Bensby
  • Sofia Feltzing
  • J. A. Johnson
  • A. Gal-Yam
  • A. Udalski
  • A. Gould
  • C. Han
  • Daniel Adén
  • Jennifer Simmerer

Summary, in English

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.

Department/s

  • Lund Observatory - Undergoing reorganization

Publishing year

2009

Language

English

Pages

174-177

Publication/Series

Astrophysical Journal

Volume

699

Issue

2

Document type

Journal article

Publisher

American Astronomical Society

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • stars: abundances
  • lensing
  • stars: fundamental parameters
  • gravitational
  • Galaxy: formation
  • Galaxy: evolution
  • Galaxy: bulge

Status

Published

Research group

  • Observational and Theoretical Astrophysics

ISBN/ISSN/Other

  • ISSN: 0004-637X