Low Temperature Rosseland Opacities
Session 55 -- Pulsating Variables/Stellar Models
Display presentation, Thursday, 2, 1994, 9:20-6:30

## [55.10] Low Temperature Rosseland Opacities

D. R. Alexander (Indiana Univ. \& Wichita St. Univ.)

A new, comprehensive set of low temperature opacity data for atoms and molecules has been assembled. From this basic data set, Rosseland and Planck mean opacities have been computed for temperatures between 12,500 K and 700 K. In addition to the standard continuous absorbers, atomic line absorption (with more than 8 million lines), molecular line absorption (with nearly 60 million lines), and grain absorption and scattering (by silicates, iron, carbon, and SiC) have been included. The absorption due to lines is computed monochromatically and included in the mean with the Opacity Sampling technique. Grains are assumed to form in chemical equilibrium and to form into a continuous distribution of ellipsoids which are ramdomly oriented.

\\ Agreement of these opacities with other recent tabulations of opacities (including OP (M. J. Seaton 1994, MNRAS\/ , 266 , 805) and OPAL (F. J. Rogers \& C. A. Iglesias 1992, {\it ApJS\/}, 79 , 507)) for temperatures above 5,000 K is excellent. It is shown that opacities which neglect molecules become unreliable for temperatures below 5,000 K. Similarly, grains must be included in the computation for temperatures below 1,000 - 1,700 K, depending upon the density.

\\ Opacity tables can be prepared for a wide variety of chemical compositions, and will be provided upon request. This research is supported by NSF grant AST-9217946.