Radiative accelerations for evolutionary model calculations

Monochromatic opacities from the OPAL database have been used to calculate radiative accelerations for the 21 included chemical species. The 10(4) frequencies used are sufficient to calculate the radiative accelerations of many elements for T > 10(5) K, using frequency sampling. This temperature limit is higher for less abundant elements. As the abundances of Fe, He, or O are varied, the radiative acceleration of other elements changes, since abundant elements modify the frequency dependence of the radiative flux and the Rosseland opacity. Accurate radiative accelerations for a given element can only be obtained by allowing the abundances of the species that contribute most to the Rosseland opacity to vary during the evolution and recalculating the radiative accelerations 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 momentum given to the electron in a photoionization. Such effects are evaluated using atomic data from Opacity Project, and correction factors are given.