The temporal evolution of neutron-capture elements in the Galactic discs

Abstract

Important insights into the formation and evolution of the Galactic disc(s)\nare contained in the chemical compositions of stars. We analysed\nhigh-resolution and high signal to noise HARPS spectra of 79 solar twin stars\nin order to obtain precise determinations of their atmospheric parameters, ages\n($\\sigma$$\\sim$0.4 Gyr) and chemical abundances ($\\sigma$$<$0.01~dex) of 12\nneutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy).\nThis valuable dataset allows us to study the [X/Fe]-age relations over a time\ninterval of $\\sim$10 Gyr and among stars belonging to the thin and thick discs.\nThese relations show that i) the $s$-process has been the main channel of\nnucleosynthesis of $n$-capture elements during the evolution of the thin disc;\nii) the thick disc is rich in $r$-process elements which suggests that its\nformation has been rapid and intensive. %; iii) a chemical continuity between\nthe thin and thick discs is evident in the abundances of Ba. In addition, the\nheavy (Ba, La, Ce) and light (Sr, Y, Zr) $s$-process elements revealed details\non the dependence between the yields of AGB stars and the stellar mass or\nmetallicity. Finally, we confirmed that both [Y/Mg] and [Y/Al] ratios can be\nemployed as stellar clocks, allowing ages of solar twin stars to be estimated\nwith an average precision of $\\sim$0.5~Gyr.\n