The Gaia-ESO Survey: {\alpha}-abundances of metal-poor stars

TL;DR

This study analyzes the ratio of low-{ extalpha} to high-{ extalpha} stars in the Galactic halo using Gaia-ESO data, revealing insights into star formation environments and their distribution.

Contribution

It provides the first detailed measurement of the low-{ extalpha} to high-{ extalpha} star ratio in the Galactic halo with no systematic trends observed.

Findings

The low-{ extalpha} to high-{ extalpha} ratio is approximately 0.28.

About 15% of metal-poor stars formed in low star formation rate environments.

The ratio shows no significant variation with metallicity or Galactic position.

Abstract

We performed a detailed study of the ratio of low-{\alpha} to high-{\alpha} stars in the Galactic halo as observed by the Gaia-ESO Survey. Using a sample of 381 metal-poor stars from the second internal data release, we found that the value of this ratio did not show evidence of systematic trends as a function of metallicity, surface gravity, Galactic latitude, Galactic longitude, height above the Galactic plane, and Galactocentric radius. We conclude that the {\alpha}-poor/{\alpha}-rich value of 0.28 $\pm$ 0.08 suggests that in the inner halo, the larger portion of stars were formed in a high star formation rate environment, and about 15% of the metal-poor stars originated from much lower star formation rate environments.