Osmium is a third-peak neutron-capture element predominantly produced by the rapid (r-) process, and it is a valuable tracer of early Galactic chemical enrichment. However, osmium abundance measurements in Galactic stars remain limited due to observational challenges. We present new osmium abundances for 23 stars at intermediate metallicities (−2.5≤ Fe/H ≤−1.0) within the framework of the MINCE (Measuring at Intermediate Metallicity Neutron-Capture Elements) project. A standard abundance analysis was carried out using one-dimensional LTE model atmospheres and the optical Os I line at 479 nm observed in high-quality UVES spectra. The derived Os/Fe ratio exhibits an anticorrelation with Fe/H, supporting efficient r-process enrichment during the early phases of the Milky Way’s evolution. We also investigated Os abundances across different Galactic components, finding that halo and Gaia–Sausage–Enceladus stars are more Os-rich than thick-disk stars. A comparison between Os and europium abundances supports a common r-process origin for these elements at intermediate metallicities.
Lucertini et al. (Thu,) studied this question.