The R-Process Alliance: First Magellan/MIKE Release from the Southern Search for R-process-enhanced Stars*

Abstract

Extensive progress has recently been made in our understanding of heavy-element production via the r -process in the universe, specifically with the first observed neutron star binary merger (NSBM) event associated with the gravitational-wave signal detected by LIGO, GW170817. The chemical abundance patterns of metal-poor r -process-enhanced stars provide key evidence for the dominant site(s) of the r -process and whether NSBMs are sufficiently frequent or prolific r -process sources to be responsible for the majority of r -process material in the universe. We present atmospheric stellar parameters (using a nonlocal thermodynamic equilibrium analysis) and abundances from a detailed analysis of 141 metal-poor stars carried out as part of the R -Process Alliance (RPA) effort. We obtained high-resolution “snapshot” spectroscopy of the stars using the MIKE spectrograph on the 6.5 m Magellan Clay telescope at Las Campanas Observatory in Chile. We find 10 new highly enhanced r -II (with [Eu/Fe] > +1.0), 62 new moderately enhanced r -I (+0.3 +0.5) and five new r / s (0.0