INTERPOLATIONS OF ROSSELAND-MEAN OPACITIES FOR VARIABLE-X AND VARIABLE-Z

For fixed relative abundances of 'metal' atoms, stellar compositions a re specified by mass fractions X for hydrogen and Z for metals (the he lium mass fraction being Y=1-X-Z). Rosseland-mean opacities depend on temperature, T, density, rho, and chemical compositions. Interpolation s in T and rho were discussed in a previous paper. The present paper i s concerned with interpolations in X and Z. The opacities are calculat ed on a grid of (X, Z) values together with information giving derivat ives of opacities with respect to X and Z. Opacities for any required value of X and Z can then be obtained using bicubic interpolations. Th e opacity tables, and codes for making interpolations, are available a t the Centre de Donnees de Strasbourg (CDS).