The EMBLA Survey -- Metal-poor stars in the Galactic bulge

TL;DR

The EMBLA Survey identified and analyzed the chemical compositions of the most metal-poor stars in the Galactic bulge, revealing unique abundance patterns that differ from halo stars, and providing insights into the Galaxy's early formation.

Contribution

This study presents the first detailed abundance analysis of metal-poor bulge stars using high-resolution spectroscopy, highlighting their distinct chemical signatures.

Findings

Bulge stars show different chemical patterns from halo stars at similar metallicities.

Absence of carbon-enhanced metal-poor stars in the bulge.

Large scatter in alpha-element abundances among bulge stars.

Abstract

Cosmological models predict the oldest stars in the Galaxy should be found closest to the centre of the potential well, in the bulge. The EMBLA Survey successfully searched for these old, metal-poor stars by making use of the distinctive SkyMapper photometric filters to discover candidate metal-poor stars in the bulge. Their metal-poor nature was then confirmed using the AAOmega spectrograph on the AAT. Here we present an abundance analysis of 10 bulge stars with -2.8<[Fe/H]<-1.7 from MIKE/Magellan observations, in total determining the abundances of 22 elements. Combining these results with our previous high-resolution data taken as part of the Gaia-ESO Survey, we have started to put together a picture of the chemical and kinematic nature of the most metal-poor stars in the bulge. The currently available kinematic data is consistent with the stars belonging to the bulge, although more accurate measurements are needed to constrain the stars' orbits. The chemistry of these bulge stars deviates from that found in halo stars of the same metallicity. Two notable differences are the absence of carbon-enhanced metal-poor bulge stars, and the alpha-element abundances exhibit a large intrinsic scatter and include stars which are underabundant in these typically enhanced elements.