SHAO Astrophysics Colloquium

Title: The Origin of the Astrophysical r-Process

Speaker: Timothy C. Beers (Univ. of Notre Dame)

Time: 3:00 pm, May 9 (Thursday)

Location: Lecture Hall, 3rd floor

Abstract: There are presently some 25 highly r-process-element-enhanced metal-poor (r-II) stars known in the Galactic halo, roughly twenty-five years after their first recognition. These stars exhibit enhancements of their r-process-element to iron ratios, relative to Solar ratios, by a factor of 10 to 100+ ([r-element/Fe] > +1.0). Despite their very low metallicities ([Fe/H < –2.0), these stars exhibit an apparently universal [r-element/Fe] pattern that is very well-matched to the Solar     r-process pattern. As such, they have long been thought to provide fundamental information on the likely astrophysical site of the r-process.  We describe a comparison of the observed properties of halo r-II stars with the remarkable recent detection of a large sample of r-II stars identified in the Ultra Faint Dwarf (UFD) galaxy Reticulum-II, and suggest that the UFD environment is the natural birthplace of essentially all r-II stars. This hypothesis has received support from the identification of lanthanide signatures in photometric and spectroscopic observations of the kilonova associated with the LIGO/Virgo neutron star merger discovery.  A new large-scale effort to dramatically increase the numbers of recognized r-II stars (from ~25-~100-150) is now underway; current results will be reported on, including the identification of numerous new bright r-II stars, severa