The R-Process Alliance: First Magellan/MIKE Release from the Southern Search for R-process-enhanced Stars
Ezzeddine, Rana, Rasmussen, Kaitlin, Frebel, Anna L., Chiti, Anirudh, Hinojisa, Karina, Placco, Vinicius M., Ji, Alexander P., Beers, Timothy C., Hansen, Terese T., Roederer, Ian U., Sakari, Charli M., Melendez, Jorge
Abstract
© 2020. The American Astronomical Society. All rights reserved.. 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 < [Eu/Fe] = +1.0), and 17 new limited-r ([Eu/Fe] < +0.3) stars. Among those, we find 17 new carbon-enhanced metal-poor (CEMP) stars, of which five are CEMP-no. We also identify one new s-process-enhanced ([Ba/Eu] > +0.5) and five new r/s (0.0 < [Ba/Eu] < +0.5) stars. In the process, we discover a new ultra-metal-poor (UMP) star at [Fe/H] = -4.02. One of the r-II stars shows a deficit in a and Fe-peak elements, typical of dwarf galaxy stars. Our search for r-process-enhanced stars by RPA efforts has already roughly doubled the known r-process sample.