Grain Physics and Rosseland Mean Opacities

TL;DR

This paper investigates how various assumptions about grain physics, such as size distribution and porosity, influence Rosseland mean opacities in astrophysical environments, highlighting the impact of grain-to-gas ratios.

Contribution

It systematically examines the effects of grain size distribution, porosity, and composition assumptions on Rosseland mean opacities in oxygen-rich environments.

Findings

Changing grain size distribution has marginal effect on opacity.

Porosity and composition of grains significantly affect opacity.

Grain-to-gas ratio variations predictably alter mean opacity.

Abstract

Tables of mean opacities are often used to compute the transfer of radiation in a variety of astrophysical simulations from stellar evolution models to proto-planetary disks. Often tables, such as Ferguson et al. (2005), 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 difference in the mean opacity between solid homogenous grains and grains that are porous or conglomorations of several species. Changing the amount of grain opacity included in the mean by assuming a grain-to-gas ratio significantly affects the mean opacity, but in a predictable way.