Radiative opacities for carbon- and oxygen-rich mixtures

Abstract

Recent OPAL calculations have obtained significant differences in the Rosseland mean opacities compared with earlier Los Alamos work. These new opacities have had a favorable impact on several astrophysical problems, but the efforts have concentrated on hydrogen main-sequence stars or stellar envelopes. The present calculations consider carbon- and oxygen-rich mixtures. It is shown that, for such mixtures, the Coulomb corrections beyond the weak-coupling approximation are not negligible in the ionization-balance calculations when Rosseland mean opacities are computed. As for hydrogen-rich compositions, the hydrogen-depleted mixtures can show factors of 2-3 enhancements in the opacity compared with the Los Alamos results at temperatures of a few hundred thousand degrees. For temperatures above a million degrees there are opacity increases as well as decreases of approximately 20 percent, depending on density. Tables of Rosseland mean opacities are provided that allow accurate interpolation for compositions of arbitrary amounts of hydrogen, carbon, and oxygen.