RADIATIVE ACCELERATIONS FOR EVOLUTIONARY MODEL-CALCULATIONS

Monochromatic opacities from the OPAL database have been used to calcu late radiative accelerations for the 21 included chemical species. The 10(4) frequencies used are sufficient to calculate the radiative acce lerations of many elements for T > 10(5) K, using frequency sampling. This temperature limit is higher for less abundant elements. As the ab undances of Fe, He, or O are varied, the radiative acceleration of oth er elements changes, since abundant elements modify the frequency depe ndence of the radiative flux and the Rosseland opacity. Accurate radia tive accelerations for a given element can only be obtained by allowin g the abundances of the species that contribute most to the Rosseland opacity to vary during the evolution and recalculating the radiative a ccelerations and the Rosseland opacity during the evolution. There are physical phenomena that cannot be included in the calculations if one uses only the OPAL data. For instance, one should correct for the mom entum given to the electron in a photoionization. Such effects are eva luated using atomic data from Opacity Project, and correction factors are given.