The R-process Alliance – a new search for r-process enhanced stars

Dr. Terese Hansen

Texas A&M University

Abstract:

Roughly half of the elements in our Universe heavier than iron are produced
via the rapid neutron-capture (r-)process. After more than sixty years of
research, an astrophysical site for the r-process was confirmed with the clear
evidence of radioactive decay of r-process material observed in the SSS17a
kilonova associated with the gravitational wave signal from a neutron star
merger. However, galactic chemical evolution models and abundances from
metal-poor stars suggest that this is not the full story and multiple
r-process sites may be involved. A small fraction (~5%) of metal-poor stars
show large enhancement in r-process elements (r-II stars). These stars are
excellent laboratories for studying the r-process as the gas from which these
stars formed was polluted by at most a few enrichment events — perhaps even
a single explosion. I will present the results of abundance analysis of
r-process enhanced stars discovered in the Milky Way halo and in dwarf
galaxies and report on recent results from the R-Process Alliance
(RPA), a new effort to uncover bright metal-poor halo stars with r-process
element enhancements. The RPA has already identified >15 new r-II stars,
increasing the number of known r-II stars by over 60%. This sample includes
the brightest, most metal-rich, and most Uranium enhanced r-II stars
discovered to date.