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Extensive progress has been recently made into our understanding of heavyelement production via the $r$-process in the Universe, specifically with thefirst observed neutron star binary merger (NSBM) event associated with thegravitational wave signal detected by LIGO, GW170817. The chemical abundancepatterns of metal-poor $r$-process-enhanced stars provides key evidence intothe dominant site(s) of the $r$-process, and whether NSBMs are sufficientlyfrequent 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 Non-Local Thermodynamic Equilibrium analysis) and abundances from adetailed 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 6.5m Magellan Claytelescope 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] $\le +1.0$) and 17 new limited-$r$ ([Eu/Fe] $< +0.3$) stars. Amongthose, we find 17 new carbon-enhanced metal-poor (CEMP) stars, of which fiveare 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$) stars. In the process, wediscover a new ultra metal-poor (UMP) star at [Fe/H]=$-$4.02. One of the $r$-IIstars shows a deficit in $\alpha$ and Fe-peak elements, typical of dwarf galaxystars. Our search for $r$-process-enhanced stars by RPA efforts, has alreadyroughly doubled the known $r$-process sample.

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