The R-Process Alliance: Chemical Abundances for a Trio of r-process-enhanced Stars—One Strong, One Moderate, and One Mild*

Abstract

We present detailed chemical abundances of three new bright ( V ∼ 11), extremely metal-poor ([Fe/H] ∼ −3.0), r -process-enhanced halo red giants based on high-resolution, high-S/N Magellan /MIKE spectra. We measured abundances for 20–25 neutron-capture elements in each of our stars. J1432−4125 is among the most r -process-rich r -II stars, with [Eu/Fe] = +1.44 ± 0.11. J2005−3057 is an r -I star with [Eu/Fe] = +0.94 ± 0.07. J0858−0809 has [Eu/Fe] = +0.23 ± 0.05 and exhibits a carbon abundance corrected for an evolutionary status of [C/Fe] corr  = +0.76, thus adding to the small number of known carbon-enhanced r -process stars. All three stars show remarkable agreement with the scaled solar r -process pattern for elements above Ba, consistent with enrichment of the birth gas cloud by a neutron star merger. The abundances for Sr, Y, and Zr, however, deviate from the scaled solar pattern. This indicates that more than one distinct r -process site might be responsible for the observed neutron-capture element abundance pattern. Thorium was detected in J1432−4125 and J2005−3057. Age estimates for J1432−4125 and J2005−3057 were adopted from one of two sets of initial production ratios each by assuming the stars are old. This yielded individual ages of 12 ± 6 Gyr and 10 ± 6 Gyr, respectively.