OGLE-2009-BLG-076S: THE MOST METAL-POOR DWARF STAR IN THE GALACTIC BULGE
- European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19 (Chile)
- Lund Observatory, Box 43, SE-221 00 Lund (Sweden)
- Department of Astronomy, Ohio State University, Columbus, OH 43210 (United States)
- Benoziyo Center for Astrophysics, Weizmann Institute of Science, 76100 Rehovot (Israel)
- Warsaw University Observatory, Warszawa (Poland)
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] {approx} -0.1. However, recently, a new opportunity emerged to utilize temporary flux amplification (by factors of {approx}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.
- OSTI ID:
- 21313030
- Journal Information:
- Astrophysical Journal (Online), Vol. 699, Issue 2; Other Information: DOI: 10.1088/0004-637X/699/2/L174; Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-4357
- Country of Publication:
- United States
- Language:
- English
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