DISCREPANCIES BETWEEN OPAL AND OP OPACITIES AT HIGH-DENSITIES AND TEMPERATURES

Recent comparisons between OPAL and OP Rosseland mean opacities show g eneral good agreement, although there are some differences. In particu lar, the largest discrepancies are found at high temperatures and dens ities relevant to the solar interior. It is shown that certain photo-a bsorption cross-sections were excluded from the OP atomic data which c an contribute to the opacity at these extreme conditions. It is also s hown that OP makes approximations in the implementation of their occup ation probability formalism that reduces the number of electrons in ex cited bound states. Calculations suggest that these factors could expl ain most of the difference at high temperatures and densities.