A High-Resolution Spectrum of the Highly Magnified Bulge G-Dwarf MOA-2006-BLG-099S

TL;DR

This study presents a high-resolution spectrum of a highly magnified G-dwarf in the Galactic bulge, revealing detailed chemical abundances and providing insights into bulge stellar populations and nucleosynthesis processes.

Contribution

First detailed chemical abundance analysis of a microlensed bulge G-dwarf, including measurements of K and Zn, and comparison with bulge and halo stars.

Findings

Star has [Fe/H]=0.36, more metal-rich than bulge M giants.

Abundance ratios of alpha and iron-peak elements are similar to bulge giants.

K and Zn abundances support their production in Type II supernovae.

Abstract

We analyze a high-resolution spectrum of a microlensed G-dwarf in the Galactic bulge, acquired when the star was magnified by a factor of 110. We measure a spectroscopic temperature, derived from the wings of the Balmer lines, that is the same as the photometric temperature, derived using the color determined by standard microlensing techniques. We measure [Fe/H]=0.36 +/-0.18, which places this star at the upper end of the Bulge giant metallicity distribution. In particular, this star is more metal-rich than any bulge M giant with high-resolution abundances. We find that the abundance ratios of alpha and iron-peak elements are similar to those of Bulge giants with the same metallicity. For the first time, we measure the abundances of K and Zn for a star in the Bulge. The [K/Mg] ratio is similar to the value measured in the halo and the disk, suggesting that K production closely tracks alpha production. The [Cu/Fe] and [Zn/Fe] ratios support the theory that those elements are produced in Type II SNe, rather than Type Ia SNe. We also measured the first C and N abundances in the Bulge that have not been affected by first dredge-up. The [C/Fe] and [N/Fe] ratios are close to solar, in agreement with the hypothesis that giants experience only canonical mixing.