http://arxiv.org/abs/1401.4437
We study the relationship between age, metallicity, and alpha-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters (including non-LTE), and the survey selection effects, which are caused by observing the stars in a given photometric box. We find that the colour and magnitude cuts on the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as large as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages (0.5 to 13.5 Gyr), Galacto-centric distances from $6$ to 9.5 kpc and vertical distances above the plane 0 < |Z| < 1.5 kpc.In the context of Galaxy formation, we find that: i) the observed age-metallicity relation is nearly flat in the range of ages between 0 and 8 Gyr, ii) there is a decline in [Fe/H] for stars with ages above 9 Gyr, which is where we detect no metal-rich stars at all; this cannot be explained by the survey selection functions, iii) there is a significant scatter of [Fe/H] at any age. In agreement with earlier work in the literature, we find that radial abundance gradients change as a function of vertical distance above the plane. The Mg gradient steepens and becomes negative. There is a well-defined double-branching of Mg abundances for stars at |Z| > 300 pc above the plane: the low and high alpha-components partly overlapping in age. The dispersion of [Mg/Fe] abundances is significant at any age. In particular, the stars with ages above 9 Gyr show a broad range in both [Mg/Fe], from 0 to 0.4 dex, and metallicity, from solar to [Fe/H] ~ -1.
Mon, 20 Jan 14
23/44
You must be logged in to post a comment.