The R-process Alliance: First Magellan/MIKE Release from the Southern
  Search for R-Process-enhanced Stars
  Extensive progress has been recently made into 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 provides key evidence into
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 Non-Local 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 6.5m 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] $\le +1.0$) 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 $\alpha$ 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.
