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Sofia Feltzing

Professor

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

Författare

  • 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.

Avdelning/ar

  • Astronomi - Har omorganiserats

Publiceringsår

2009

Språk

Engelska

Sidor

174-177

Publikation/Tidskrift/Serie

Astrophysical Journal

Volym

699

Issue

2

Dokumenttyp

Artikel i tidskrift

Förlag

American Astronomical Society

Ämne

  • Astronomy, Astrophysics and Cosmology

Nyckelord

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

Aktiv

Published

Forskningsgrupp

  • Observational and Theoretical Astrophysics

ISBN/ISSN/Övrigt

  • ISSN: 0004-637X