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A Puzzle Involving Galactic Bulge Microlensing Events

J. G. Cohen, A. Gould, I. B. Thompson, S. Feltzing, T. Bensby, J. A. Johnson, W. Huang, J. MelÚndez, S. Lucatello, M. Asplund

Abstract
We study a sample of 16 microlensed Galactic bulge main sequence turnoff region stars for which high dispersion spectra have been obtained with detailed abundance analyses. We demonstrate that there is a very strong and highly statistically significant correlation between the maximum magnification of the microlensed bulge star and the value of the [Fe/H] deduced from the high resolution spectrum of each object. Physics demands that this correlation, assuming it to be real, be the result of some sample bias. We suggest several possible explanations, but are forced to reject them all, and are left puzzled. To obtain a reliable metallicity distribution in the Galactic bulge based on microlensed dwarf stars it will be necessary to resolve this issue through the course of additional observations.

Keywords
Galaxy: bulge - gravitational lensing:micro - stars: abundances

Notes
Based in part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

The Astrophysical Journal Letters
Volume 711, Number 1, Page L48
2010 March

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Instituto de Astrof├şsica e Ci├¬ncias do Espa├žo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Funda├ž├úo para a Ci├¬ncia e a Tecnologia COMPETE 2020 PORTUGAL 2020 Uni├úo Europeia