Chemical Composition of Faint (I~21 mag) Microlensed Bulge Dwarf OGLE-2007-BLG-514S

TL;DR

This study analyzes the chemical composition of a faint microlensed dwarf star in the Galactic bulge, revealing its high metallicity and abundance patterns, and compares it with bulge giants to understand stellar populations.

Contribution

It provides detailed elemental abundances for a faint bulge dwarf star and compares its chemical properties with bulge giants, highlighting similarities and differences at high metallicity.

Findings

Star has high metallicity [Fe/H] = 0.33

No alpha enhancement observed in the star

Discrepancy in Na abundance between bulge giants and dwarfs at high metallicity

Abstract

We present a high-resolution spectrum of a microlensed G dwarf in the Galactic bulge with spectroscopic temperature T_eff = 5600 +/- 180 K. This I~21 mag star was magnified by a factor ranging from 1160 to 1300 at the time of observation. Its high metallicity ([Fe/H] = 0.33 +/- 0.15) places this star at the upper end of the bulge giant metallicity distribution. Using a K-S test, we find a 1.6% probability that the published microlensed bulge dwarfs share an underlying distribution with bulge giants, properly accounting for a radial bulge metallicity gradient. We obtain abundance measurements for 15 elements and perform a rigorous error analysis that includes covariances between parameters. This star, like bulge giants with the same metallicity, shows no alpha enhancement. It confirms the chemical abundance trends observed in previously analyzed bulge dwarfs. At supersolar metallicities, we observe a discrepancy between bulge giant and bulge dwarf Na abundances.