The Gaia-ESO survey: Placing constraints on the origin of r-process elements

Context. A renewed interest in the origin of r-process elements has been stimulated by the multi-messenger observation of the gravitational event GW170817, with the detection of both gravitational waves and electromagnetic waves corresponding to the merger of two neutron stars. Such a phenomenon has been proposed as one of the main sources of the r-process. However, the origin of the r-process elements at different metallicities is still under debate.
Aims: We aim at investigate the origin of the r-process elements in the Galactic thin-disc population.
Methods: From the sixth internal data release of the Gaia-ESO, we have collected a large sample of Milky Way (MW) thin- and thick-disc stars for which abundances of Eu, O, and Mg are available. The sample consists of members of 62 open clusters (OCs), located at a Galactocentric radius between ∼5 kpc and ∼20 kpc in the disc, in the metallicity range [ − 0.5, 0.4], and covering an age interval from 0.1 to 7 Gy, and about 1300 Milky Way disc field stars in the metallicity range [ − 1.5, 0.5]. We compare the observations with the results of a chemical evolution model, in which we varied the nucleosynthesis sources for the three elements considered.
Results: Our main result is that Eu in the thin disc is predominantly produced by sources with short lifetimes, such as magneto-rotationally driven SNe. There is no strong evidence for additional sources at delayed times.
Conclusions: Our findings do not imply that there cannot be a contribution from mergers of neutron stars in other environments, as in the halo or in dwarf spheroidal galaxies, but such a contribution is not needed to explain Eu abundances at thin-disc metallicities.