# The Gaia-ESO Survey: α-abundances of metal-poor stars

Jackson-Jones, R and Jofré, P and Hawkins, K and Hourihane, A and Gilmore, G and Kordopatis, G and Worley, C and Randich, S and Vallenari, A and Bensby, T and Bragaglia, A and Flaccomio, E and Korn, AJ and Recio-Blanco, A and Smiljanic, R and Costado, MT and Heiter, U and Hill, V and Lardo, C and Laverny, PD and Guiglion, G and Mikolaitis, S and Zaggia, S and Tautvaišiene, G (2014) The Gaia-ESO Survey: α-abundances of metal-poor stars. Astronomy & Astrophysics.

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.