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

Jackson-Jones, R.; Jofré, P.; Hawkins, K.; Hourihane, A.; Gilmore, G.; Kordopatis, G.; Worley, C.; Randich, S.; Vallenari, A.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Korn, A. J.; Recio-Blanco, A.; Smiljanic, R.; Costado, M. T.; Heiter, U.; Hill, V.; Lardo, C.; de Laverny, P.; Guiglion, G.; Mikolaitis, S.; Zaggia, S.; Tautvaišiene, G.
Astronomy & Astrophysics, Volume 571, id.L5, 5 pp. (2014).


We performed a detailed study of the ratio of low-α to high-α 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 αpoorrich value of 0.28 ± 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.