Exploring nucleosynthesis in the early Universe with extremely metal-poor stars

Dr. Terese Hansen (Carnegie)
Tuesday, October 23, 2018 - 4:00pm

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. I will also 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.

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