Model Atmospheres of Late-Type Stars

Model atmospheres with solar abundances have been calculated with effective temperatures between 20000 and 40000 K and with gravities corresponding to dwarf, giant, and supergiant stars. The opacity due to water vapor was included. Convection was included by using the Böhm-Vitense mixing-length theory with the mixing length equal to the pressure-scale height. The convection begins at r <0.05 in the dwarfs and carries a considerable fraction of the total flux when r »= 1.0. In the giants and super- giants the convection does not carry a significant part of the flux until hydrogen begins to ionize at r `~` 10, although it may occur at small optical depths. The frequency dependence of the emitted fluxes is extremely nongray and does not vary simply with the effective temperature. In order to test the effects of varying the composition, two atmospheres were calculated with Te = 40000 K and logg = 2.0, with the solar metal abundances reduced by factors of 10 and 100. The emitted flux changed only slightly. In addition, two atmospheres were calculated with T~ = 30000 K and logg = 1.0, with the car- bon abundance varied. The strengths of the H20 features vary much less than the H20 abundance