Low-Temperature Opacities

Previous computations of low-temperature Rosseland and Planck mean opacities from Alexander & Ferguson are updated and expanded. The new computations include a more complete equation of state (EOS) with more grain species and updated optical constants. Grains are now explicitly included in thermal equilibrium in the EOS calculation, which allows for a much wider range of grain compositions to be accurately included than was previously the case. The inclusion of high-temperature condensates such as Al₂O₃ and CaTiO₃ significantly affects the total opacity over a narrow range of temperatures before the appearance of the first silicate grains. The new opacity tables are tabulated for temperatures ranging from 30,000 to 500 K with gas densities from 10^-4 to 10^-19 g cm^-3. Comparisons with previous Rosseland mean opacity calculations are discussed. At high temperatures, the agreement with OPAL and Opacity Project is quite good. Comparisons at lower temperatures are more divergent as a result of differences in molecular and grain physics included in different calculations. The computation of Planck mean opacities performed with the opacity sampling method is shown to require a very large number of opacity sampling wavelength points; previously published results obtained with fewer wavelength points are shown to be significantly in error. Methods for requesting or obtaining the new tables are provided.