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Title:
OGLE-2009-BLG-076S: The Most Metal-Poor Dwarf Star in the Galactic Bulge
Authors:
Bensby, T.; Feltzing, S.; Johnson, J. A.; Gal-Yam, A.; Udalski, A.; Gould, A.; Han, C.; Adén, D.; Simmerer, J.
Affiliation:
AA(European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile ), AB(Lund Observatory, Box 43, SE-221 00 Lund, Sweden ), AC(Department of Astronomy, Ohio State University, Columbus, OH 43210, USA ), AD(Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel ), AE(Warsaw University Observatory, Warszawa, Poland ), AF(Department of Astronomy, Ohio State University, Columbus, OH 43210, USA ), AG(Department of Physics, Chungbuk National University, Chongju, Republic of Korea ), AH(Lund Observatory, Box 43, SE-221 00 Lund, Sweden ), AI(Lund Observatory, Box 43, SE-221 00 Lund, Sweden )
Publication:
The Astrophysical Journal Letters, Volume 699, Issue 2, pp. L174-L177 (2009). (ApJL Homepage)
Publication Date:
07/2009
Origin:
IOP
ApJ Keywords:
Galaxy: bulge, Galaxy: evolution, Galaxy: formation, gravitational lensing, stars: abundances, stars: fundamental parameters
DOI:
10.1088/0004-637X/699/2/L174
Bibliographic Code:
2009ApJ...699L.174B

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] ≈ -0.1. However, recently, a new opportunity emerged to utilize temporary flux amplification (by factors of ~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.

Based on observations made with the European Southern Observatory telescopes, Program ID 082.B-0453(B).

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