The likely outcome of a compact object merger event is a central black hole surrounded by a rapidly accreting torus of debris. This disk of debris is a rich source of element synthesis, the outcome of which is needed to predict electromagnetic counte
rparts of individual events and to understand the contribution of mergers to galactic chemical evolution. Here we study disk outflow nucleosynthesis in the context of a two-dimensional, time-dependent black hole-neutron star merger accretion disk model. We use two time snapshots from this model to examine the impact of the evolution of the neutrino fluxes from the disk on the element synthesis. While the neutrino fluxes from the early-time disk snapshot appear to favor neutron-rich outflows, by the late-time snapshot the situation is reversed. As a result we find copious production of Nickel-56 in the outflows.
Simulations of r-process nucleosynthesis require nuclear physics information for thousands of neutron-rich nuclear species from the line of stability to the neutron drip line. While arguably the most important pieces of nuclear data for the r-process
are the masses and beta decay rates, individual neutron capture rates can also be of key importance in setting the final r-process abundance pattern. Here we consider the influence of neutron capture rates in forming the A~80 and rare earth peaks.
We consider hot accretion disk outflows from black hole - neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three dimensional numerical model of a black hole - neutron star merger and calculate the neutrino and
antineutrino fluxes emitted from the resulting accretion disk. We then follow the element synthesis in material outflowing the disk along parameterized trajectories. We find that at least a weak r-process is produced, and in some cases a main r-process as well. The neutron-rich conditions required for this production of r-process nuclei stem directly from the interactions of the neutrinos emitted by the disk with the free neutrons and protons in the outflow.
We investigate the impact of neutron capture rates near the A=130 peak on the $r$-process abundance pattern. We show that these capture rates can alter the abundances of individual nuclear species, not only in the region of A=130 peak, but also throu
ghout the abundance pattern. We discuss the nonequilibrium processes that produce these abundance changes and determine which capture rates have the most significant impact.
