Context. Precise stellar ages from asteroseismology have become available and can help setting stronger constraints on the evolution of the Galactic disc components. Recently, asteroseismology has confirmed a clear age difference in the solar annulus between two distinct sequences in the [α/Fe] versus [Fe/H] abundance ratios relation: the high-α and low-α stellar populations. Aims. We aim at reproducing these new data with chemical evolution models including different assumptions for the history and number of accretion events. Methods. We tested two different approaches: a revised version of the "two-infall" model where the high-α phase forms by a fast gas accretion episode and the low-α sequence follows later from a slower gas infall rate, and the parallel formation scenario where the two disc sequences form coevally and independently. Results. The revised "two-infall" model including uncertainties in age and metallicity is capable of reproducing: i) the [α/Fe] vs. [Fe/H] abundance relation at different Galactic epochs, ii) the age−metallicity relation and the time evolution [α/Fe]; iii) the age distribution of the high-α and low-α stellar populations, iv) the metallicity distribution function. The parallel approach is not capable of properly reproduce the stellar age distribution, in particular at old ages. Conclusions. The best chemical evolution model is the revised "two-infall" one, where a consistent delay of ∼4.3 Gyr in the beginning of the second gas accretion episode is a crucial assumption to reproduce stellar abundances and ages.

We study the chemical evolution of the thick and thin discs of the Galaxy by comparing detailed chemical evolution models with recent data from the AMBRE Project. The data suggest that the stars in the thick and thin discs form two distinct sequences with the thick disc stars showing higher [α/Fe] ratios. We adopt two different approaches to model the evolution of thick and thin discs. In particular, we adopt: i) a two-infall approach where the thick disc forms fast and before the thin disc and by means of a fast gas accretion episode, whereas the thin disc forms by means of a second accretion episode on a longer timescale; ii) a parallel approach, where the two discs form in parallel but at different rates. By comparing our model results with the observed [Mg/Fe] vs. [Fe/H] and the metallicity distribution functions in the two Galactic components, we conclude that the parallel approach can account for a group of α-enhanced metal rich stars present in the data, whereas the two-infall approach cannot explain these stars unless they are the result of stellar migration. In both approaches, the thick disc has formed on a timescale of accretion of 0.1 Gyr, whereas the thin disc formed on a timescale of 7 Gyr in the solar region. In the two-infall approach a gap in star formation between the thick and thin disc formation of several hundreds of Myr should be present, at variance with the parallel approach where no gap is present.

In this paper, we study the formation and chemical evolution of the Milky Way disc with particular focus on the abundance patterns ([α/Fe] vs. [Fe/H]) at different Galactocentric distances, the present-time abundance gradients along the disc and the time evolution of abundance gradients. We consider the chemical evolution models for the Galactic disc developed by Grisoni et al. (2017) for the solar neighborhood, both the two-infall and the one-infall ones, and we extend our analysis to the other Galactocentric distances. In particular, we examine the processes which mainly influence the formation of the abundance gradients: the inside-out scenario, a variable star formation efficiency, and radial gas flows. We compare our model results with recent abundance patterns obtained along the Galactic disc from the APOGEE survey and with abundance gradients observed from Cepheids, open clusters, HII regions and PNe. We conclude that the inside-out scenario is a key ingredient, but cannot be the only one to explain abundance patterns at different Galactocentric distances and abundance gradients. Further ingredients, such as radial gas flows and variable star formation efficiency, are needed to reproduce the observed features in the thin disc. The evolution of abundance gradients with time is also shown, although firm conclusions cannot still be drawn.

We study the evolution of Milky Way thick and thin discs in the light of the most recent observational data. In particular, we analyze abundance gradients of O, N, Fe and Mg along the thin disc as well as the [Mg/Fe] vs. [Fe/H] relations and the metallicity distribution functions at different Galactocentric distances. We run several models starting from the two-infall paradigm, assuming that the thick and thin discs formed by means of two different infall episodes, and we explore several physical parameters, such as radial gas flows, variable efficiency of star formation, different times for the maximum infall onto the disc, different distributions of the total surface mass density of the thick disc and enriched gas infall. Our best model suggests that radial gas flows and variable efficiency of star formation should be acting together with the inside-out mechanism for the thin disc formation. The timescale for maximum infall onto the thin disc, which determines the gap between the formation of the two discs, should be tmax ≃ 3.25 Gyr. The thick disc should have an exponential, small scale length density profile and gas infall on the inner thin disc should be enriched. We compute also the evolution of Gaia-Enceladus system and study the effects of possible interactions with the thick and thin discs. We conclude that the gas lost by Enceladus or even part of it could have been responsible for the formation of the thick disc but not the thin disc.