Vol. 565
In section 5. Galactic structure, stellar structure and populations

The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk

This paper presents stellar parameters and abundances for the 144 FGK stars observed in the Galactic disc during the initial six months of the Gaia-ESO survey. The main goal is to study the relationship between age, metallicity, and spatial distribution for these stars. Thus, the sample includes a wide range of ages (0.5 Gyr to 13.5 Gyr); Galactocentric distances (6 kpc to 9.5 kpc), and vertical distances from the plane (0 < |Z| < 1.5 kpc).

The authors find a significant scatter in [Fe/H] measurements at all ages, but the age-metallicity relation is nearly flat for stars between 0 Gyr and 8 Gyrs old. For older ages a decrease in the mean [Fe/H] is observed, with a clear absence of metal-rich stars. In contrast [Mg/Fe] values, which represent α-elements in this study, also exhibit significant scatter, but the values show an overall mean increase with increasing age. In agreement with earlier work, the authors find that radial abundance gradients change as a function of vertical distance from the plane, and the inner disk is not only more Mg-rich than the outer disk, but also older. This initial dataset illustrates the potential of the Gaia-ESO Survey. The much larger datasets from the upcoming Gaia-ESO data releases will allow us to distinguish among the many theories describing Galactic disk formation.