The R-Process Alliance: Analysis of limited-r stars

Context. In recent years, the R -Process Alliance (RPA) has conducted a successful search for stars that are enhanced in elements produced by the rapid neutron-capture ( r -)process. In particular, the RPA has uncovered a number of stars that are strongly enriched in light r -process elements, such as Sr, Y, and Zr. These so-called limited- r stars were investigated to explore the astrophysical production site(s) of these elements. Aims. We investigate the possible formation sites for light neutron-capture elements by deriving detailed abundances for neutron-capture elements from high-resolution spectra with a high signal-to-noise ratio of three limited- r stars. Methods. We conducted a kinematic analysis and a 1D local thermodynamic equilibrium spectroscopic abundance analysis of three stars. Furthermore, we calculated the lanthanide mass fraction ( X La ) of our stars and of limited- r stars from the literature. Results. We found that the abundance pattern of neutron-capture elements of limited- r stars behaves differently depending on their Ba/Eu ratios, and we suggest that this should be taken into account in future investigations of their abundances. Furthermore, we found that the X La of limited- r stars is lower than that of the kilonova AT2017gfo. The latter seems to be in the transition zone between limited- rX La and that of r -I and r -II stars. Finally, we found that unlike r -I and r -II stars, the current sample of limited- r stars is largely born in the Galaxy and is not accreted.