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 6.5 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 ] \leq + 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 .