Grain physics and rosseland mean opacities

Tables of mean opacities are often used to compute the transfer of radiation in a variety of astrophysical simula-tions, from stellar evolution models to protoplanetary disks. Often these tables, such as those in a recent paper by Ferguson and coworkers, are computed with a predetermined set of physical assumptions that may or may not be valid for a specific application. This paper explores the effects of several assumptions of grain physics on the Rosseland mean opacity in an oxygen-rich environment. We find that changing the distribution of grain sizes, either the power-law exponent or the shape of the distribution, has a marginal effect on the total mean opacity. We also explore the dif-ference in the mean opacity between solid homogenous grains and grains that are porous or conglomerations of several species. Changing the amount of grain opacity included in the mean by assuming a grain-to-gas ratio sig-nificantly affects the mean opacity, but in a predictable way.