The Gaia-ESO Survey: Oxygen abundance in the Galactic thin and thick
  disks
  We analyze the oxygen abundances of a stellar sample representative of the
two major Galactic populations: the thin and thick disks. The aim is to
investigate the differences between members of the Galactic disks and to
contribute to the understanding on the origin of oxygen chemical enrichment in
the Galaxy. The analysis is based on the [O\,{\sc i}]=6300.30\,\AA~ oxygen line
in HR spectra ($R\sim$52,500) obtained from the GES Survey. By comparing the
observed spectra with a theoretical dataset, computed in LTE with the SPECTRUM
synthesis and ATLAS12 codes, we derive the oxygen abundances of 516 FGK dwarfs
for which we have previously measured carbon abundances. Based on kinematic,
chemical and dynamical considerations we identify 20 thin and 365 thick disk
members. We study potential trends of both subsamples in terms of their
chemistry ([O/H], [O/Fe], [O/Mg], and [C/O] versus [Fe/H] and [Mg/H]), age, and
position in the Galaxy. Main results are: (a) [O/H] and [O/Fe] ratios versus
[Fe/H] show systematic differences between thin and thick disk stars with
enhanced O abundance of thick disk stars with respect to thin disk members and
a monotonic decrement of [O/Fe] with increasing metallicity, even at metal-rich
regime; (b) a smooth correlation of [O/Mg] with age in both populations,
suggesting that this abundance ratio can be a good proxy of stellar ages within
the Milky Way; (c) thin disk members with [Fe/H]$\simeq0$ display a [C/O] ratio
smaller than the solar value, suggesting a possibly outward migration of the
Sun from lower Galactocentric radii.
