Atomospheres of red supergiant stars, 2

The possibility of applying model atmospheres for the interpretation of observed spectral energy distributions is examined in the case of Betelgeuse as an example. The effect of atomic line absorptions is taken into account by an empirical line-blocking analysis, while the line-blanketing effect due to molecular absorption is considered in the construction of model atmospheres. It is shown that the dependence of the predicted emergent fluxes on effective temperature makes it possible to estimate the effective temperature within +-100K. By considering other uncertainties in our models, we obtain T sub(eff)(αOri) = 3900+-150K from an analysis of the observed spectral energy distributions corrected for interstellar reddening with A sub(v) = 0.7 mag. The analysis is carried out on the relative flux distribution and hence the result is independent of the angular diameter. The final models used in this analysis are based on a possibly realistic chemical composition for Betelgeuse. It is also shown that the line spectrum of Betelgeuse can be best understood by models with T sub(eff) near 4000K. On the other hand, among about 20 values of the angular diameter now available, the minimum value of theta sub(UD) = 0.034, with proper correction for limb-darkening, gives an empirical effective temperature of about 4000K. The minimum angular diameter probably represents an observation with the highest resolution ever attained. Then, it can be concluded that the spectral energy distribution, line spectrum, and angular diameter of Betelgeuse can be consistently understood by a model with T sub(eff) -- 4000K. (auth.)