Low‐Temperature Opacities

Previous computations of low temperature Rosseland and Planck mean opacitiesfrom Alexander & Ferguson (1994) are updated and expanded. The new computationsinclude a more complete equation of state with more grain species and updatedoptical constants. Grains are now explicitly included in thermal equilibrium inthe equation of state calculation, which allows for a much wider range of graincompositions to be accurately included than was previously the case. Theinclusion of high temperature condensates such as Al$_2$O$_3$ and CaTiO$_3$significantly affects the total opacity over a narrow range of temperaturesbefore the appearance of the first silicate grains. The new opacity tables are tabulated for temperatures ranging from 30000 K to500 K with gas densities from 10$^{-4}$ g cm$^{-3}$ to 10$^{-19}$ g cm$^{-3}$.Comparisons with previous Rosseland mean opacity calculations are discussed. Athigh temperatures, the agreement with OPAL and Opacity Project is quite good.Comparisons at lower temperatures are more divergent as a result of differencesin molecular and grain physics included in different calculations. Thecomputation of Planck mean opacities performed with the opacity sampling methodare shown to require a very large number of opacity sampling wavelength points;previously published results obtained with fewer wavelength points are shown tobe significantly in error. Methods for requesting or obtaining the new tablesare provided.Comment: 39 pages with 12 figures. To be published in ApJ, April 200