The Gaia-ESO Survey: the most metal-poor stars in the Galactic bulge

TL;DR

This paper reports the discovery and detailed chemical analysis of the most metal-poor stars in the Galactic bulge, revealing similarities to halo stars and highlighting the potential for studying the Galaxy's oldest populations.

Contribution

First high-resolution spectroscopic analysis of extremely metal-poor bulge stars, demonstrating their chemical similarities to halo stars and expanding understanding of Galactic formation.

Findings

Bulge stars with -2.72<=[Fe/H]<=-2.48 identified and analyzed.

Chemical compositions similar to halo stars at comparable metallicities.

Some stars exhibit unusual alpha-element ratios.

Abstract

We present the first results of the EMBLA survey (Extremely Metal-poor BuLge stars with AAOmega), aimed at finding metal-poor stars in the Milky Way bulge, where the oldest stars should now preferentially reside. EMBLA utilises SkyMapper photometry to pre-select metal-poor candidates, which are subsequently confirmed using AAOmega spectroscopy. We describe the discovery and analysis of four bulge giants with -2.72<=[Fe/H]<=-2.48, the lowest metallicity bulge stars studied with high-resolution spectroscopy to date. Using FLAMES/UVES spectra through the Gaia-ESO Survey we have derived abundances of twelve elements. Given the uncertainties, we find a chemical similarity between these bulge stars and halo stars of the same metallicity, although the abundance scatter may be larger, with some of the stars showing unusual [{\alpha}/Fe] ratios.