We study the relationship between age, metallicity, andα-enhancement of FGK stars in the Galactic disk. The results arebased upon the analysis of high-resolution UVES spectra from theGaia-ESO large stellar survey. We explore the limitations of theobserved dataset, i.e. the accuracy of stellar parameters and theselection effects that are caused by the photometric targetpreselection. We find that the colour and magnitude cuts in the surveysuppress old metal-rich stars and young metal-poor stars. Thissuppression may be as high as 97% in some regions of the age-metallicityrelationship. The dataset consists of 144 stars with a wide range ofages from 0.5 Gyr to 13.5 Gyr, Galactocentric distances from 6 kpcto 9.5kpc, and vertical distances from the plane 0 <|Z| <1.5 kpc. Onthis basis, we find that i) the observed age-metallicity relation isnearly flat in the range of ages between 0 Gyr and 8 Gyr; ii) at agesolder than 9 Gyr, we see a decrease in [Fe/H] and a clear absence ofmetal-rich stars; this cannot be explained by the survey selectionfunctions; iii) there is a significant scatter of [Fe/H] at any age; andiv) [Mg/Fe] increases with age, but the dispersion of [Mg/Fe] at ages>9 Gyr is not as small as advocated by some other studies. Inagreement with earlier work, we find that radial abundance gradientschange as a function of vertical distance from the plane. The [Mg/Fe]gradient steepens and becomes negative. In addition, we show that theinner disk is not only more α-rich compared to the outer disk, butalso older, as traced independently by the ages and Mg abundances of stars.Based on observations made with the ESO/VLT, at Paranal Observatory,under programme 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey).
- stars: abundances
- stars: fundamental parameters
- solar neighborhood
- Galaxy: disk
- Galaxy: formation