SPIN-ORBIT INTERACTION EFFECTS ON THE ROSSELAND MEAN OPACITY

Recently published opacity tables for astrophysical mixtures using the OPAL code showed significant differences when compared to the commonly used Los Alamos results. An important finding of the OPAL calculations was a large opacity enhancement (approximately factors of 3) in the few hundred-thousand degree temperature range. This new opacity bump is a consequence of improvements in the atomic data generation. Specifically, the configuration term splitting in OPAL was done in the pure LS-coupling approximation which is essentially neglected in the Los Alamos calculations. However, for heavier elements such as Fe, spin-orbit interactions are small but not negligible; consequently, pure LS-coupling breaks down. The main impact of the spin-orbit interaction is to enhance significantly the opacity in the region of the new Z bump (as much as 50%) but only at low densities. New Rosseland mean opacity tables with intermediate coupling for the Fe have been tabulated. Although a metal composition based on recent analysis of solar observations is assumed as standard, opacity tables for mixtures with different relative metal abundances are possible. In addition, the previous tables are extended to lower and higher densities as well as higher metallicity.