Speaker: Andrew Steiner (University of Minnesota)

Nuclear Astrophysics in Two Acts: r-Process Nucleosynthesis in Neutrino-Driven Winds and the Nuclear Symmetry Energy

In the first portion of this talk, we revisit the problem of r-process nucleosynthesis in neutrino driven winds. The boundary conditions for the neutrino-driven wind near the neutron star surface are determined through the construction of an ``injection region''. Our models of the wind duplicate the results obtained from hydrodynamic simulations to within ten percent. The neutron to seed ratio, and hence the ability of the system to reach the r-process peaks at A=130 and A=90, is determined self-consistently with the wind. This self-consistency is achieved by ensuring that the nuclear abundances track the properties of the wind as the radius increases. This entire procedure allows for a determination of the r-process abundances given the properties of the neutron star and the accompanying neutrino emission. In the second portion, the influence of isospin dependence on the structure of neutron stars and nuclei will be explored. We utilize both field theoretical and potential model (Akmal, et. al (APR), and Skyrme) approaches for the description of the equation of state to study neutron stars, semi-infinite matter, and finite nuclei. This is combined with an analytical study of the nuclear surface which reproduces results at the 20 percent level. We conclude that: 1) a fit to APR gives reasonable results for the binding energies and charge radii of doubly-magic nuclei, 2) relativistic models with sufficient flexibility to describe variations in the symmetry energy allow for neutron star radii as small as 9 km but that non-relativistic models can easily result in even smaller neutron star radii, 3) a combination of a neutron star radius measurement together with a measurement of the neutron skin thickness of lead will lead to a constraint on the nuclear equation of state, 4) our analytical formalism is a useful tool for understanding qualitatively the relationship between the density dependence of the symmetry energy and the properties of the equation of state of both nuclear matter and neutron star matter.