Important insights into the formation and evolution of the Galactic disc(s) are contained in the chemical compositions of stars. We analysed high-resolution and high signal-to-noise HARPS spectra of 79 solar twin stars in order to obtain precise determinations of their atmospheric parameters, ages ({sigma}~0.4Gyr) and chemical abundances ({sigma}<0.01dex) of 12 neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd and Dy). This valuable data set allows us to study the [X/Fe]-age relations over a time interval of ~10Gyr and among stars belonging to the thin and thick discs. These relations show that (i) the s-process has been the main channel of nucleosynthesis of n-capture elements during the evolution of the thin disc; (ii) the thick disc is rich in r-process elements which suggests that its formation has been rapid and intensive. In addition, the heavy (Ba, La, Ce) and light (Sr, Y, Zr) s-process elements revealed details on the dependence between the yields of AGB stars and the stellar mass or metallicity. Finally, we confirmed that both [Y/Mg] and [Y/Al] ratios can be employed as stellar clocks, allowing ages of solar twin stars to be estimated with an average precision of ~0.5Gyr.

Cone search capability for table J/MNRAS/474/2580/table3 (Chemical abundances of the n-capture elements determined for the 79 solar twin stars)

Cone search capability for table J/MNRAS/474/2580/table1 (The list of the 79 solar twins stars analysed in this paper)

Cone search capability for table J/MNRAS/474/2580/table2 (Atmospheric parameters determined through our analysis)

Cone search capability for table J/MNRAS/474/2580/table4 (Stellar ages and masses determined for the 79 solar twins)