The effect of sphericity on stellar continuous energy distribution.
Abstract
Model stellar atmospheres are constructed with the object of explaining the anomaly observed in a number of WolfRayet stars, especially HD 50896, and in at least one Of star, Puppis, that the line spectrum indicates a higher temperature than does the continuous spectrum. The models assume radiative and hydrostatic equilibrium, and local thermodynamic equilibrium. The composition is approximated by pure hydrogen, and the effects of lines are ignored. The spherical symmetry of the atmosphere is taken fully into account. It is found that the extension of the atmosphere, and the atmospheric density, depend critically upon the ratio of luminosity to mass for the model. Approximate analytic results are obtained which give a quantitative expression for this dependence. The principal result regarding the continuous spectrum is that, for the extended models, the brightness temperature is a monotonically increasing function of frequency, over the observed range, which agrees with the effective temperature near the blackbody maximum. This result is explained in terms of the effect of electron scattering on the emergent radiation. The frequency dependence of the brightness temperature is sufficient to explain the observations of Pup if a sufficiently luminous model is chosen. Such models are excluded, however, by stellar evolution theory. It is suggested that an extension of the atmosphere similar to that in luminous models may be produced by a stellar wind, but in order to affect the continuous spectrum the rate of mass loss must be much greater than that obtained by Lucy and Solomon. Subject headings: atmospheres  Oftype stars  WolfRayet stars
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1974
 DOI:
 10.1086/152800
 Bibcode:
 1974ApJ...189..273C