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Session 67 - Stars: Evolution, Atmospheres, Intrinsic.
Display session, Thursday, June 11
Atlas Ballroom,

[67.16] Low Temperature Grain Opacities

D. R. Alexander, A. Tamanai, F. Allard, J. W. Ferguson (Wichita State U.)

Optical constants for a wide variety of materials which condense at low temperatures in the atmospheres of stars and during star and planet formation have been incorporated into the calculation of low temperature opacities. The equation of state has been modified to include the condensation of grains in thermal equilibrium with the gas phase for any chemical composition. It is shown that high temperature condensates, such as Al_2O_3, can dramatically affect the opacity when they are the only solid species present. The condensation of some grain species, such as CaTiO_3, can also dramatically affect the gas phase abundance of important absorbers, such as TiO. Finally, at much lower temperatures the oxides and sulfides of iron become dominant absorbers until finally water particles begin to condense. The opacity of grains can be important in the atmospheres of the coolest dwarf stars and in brown dwarf atmospheres, leading to a significant reduction in the strength of the TiO molecular bands in the visual spectrum. Our coolest giant models also show that Al_2O_3 has condensed in the outermost, optically thin zones of those stars.

This research was supported by NASA EPSCoR grant NCC5-168 and NASA LTSA grant NAG5-3435 to Wichita State University.

Program listing for Thursday