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Fig. 1


Age–[α/Fe] relation in different regions of the Galactic disc. Upper left panel: the grey curves indicate the predictions of the multi-zone Galactic chemical-evolution model of Chiappini (2009) for the thin and thick discs, where different tracks were calculated for different Galactocentric annuli situated between 2 and 18 kpc from the Galactic Centre. The solar position is indicated in the diagram for the 6 kpc curve, the distance of the most probable birth position of the Sun (Minchev et al. 2013). Within these models, it is not possible to explain stars that fall into the grey-shaded region of the diagram: young, [α/Fe]-enhanced stars. The grey shadings provide a heuristic estimate of the typical (N = 1,2,3) uncertainties in [Mg/Fe] and age. Upper middle and right panels: the solar cylinder data from Bensby et al. (2014, and the Gaia-ESO survey (Bergemann et al. 2014; right panel) show a clear correlation between isochrone-derived age estimates and relative [α/Fe] abundances. Stars whose age and abundance estimates are 1σ-incompatible with any of the chemical evolution curves are represented by stars; 2σ-outliers are represented by pentagons. Lower panels: the same diagram for the CoRoT-APOGEE sample. Left: the LRa01 outer-disc field. Middle: the LRc01 inner-disc field, close to the Galactic plane (| ZGal | < 0.3 kpc, RGal> 6.0 kpc). Right: the LRc01 field, below the Galactic plane (ZGal< −0.3 kpc, RGal< 6.5 kpc). In this region, the fraction of young α-enhanced stars is much larger than in all other regions. Considering normal stars alone, the age-[α/Fe] relation is much flatter than locally because the CoRoT stars span a wide range in Galactocentric distances.

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