Advances in Atomic Data for Neutron-Capture Elements
  Neutron(n)-capture elements (atomic number Z>30), which can be produced in
planetary nebula (PN) progenitor stars via s-process nucleosynthesis, have been
detected in nearly 100 PNe. This demonstrates that nebular spectroscopy is a
potentially powerful tool for studying the production and chemical evolution of
trans-iron elements. However, significant challenges must be addressed before
this goal can be achieved. One of the most substantial hurdles is the lack of
atomic data for n-capture elements, particularly that needed to solve for their
ionization equilibrium (and hence to convert ionic abundances to elemental
abundances). To address this need, we have computed photoionization cross
sections and radiative and dielectronic recombination rate coefficients for the
first six ions of Se and Kr. The calculations were benchmarked against
experimental photoionization cross section measurements. In addition, we
computed charge transfer (CT) rate coefficients for ions of six n-capture
elements. These efforts will enable the accurate determination of nebular Se
and Kr abundances, allowing robust investigations of s-process enrichments in
PNe.
