Non-Lte Model Atmospheres. I. Radiative Equilibrium Models with - Alpha

We present models of stellar atmospheres of pure hydrogen in hydrostatic, radiative, and statistical equilibrium, including for the first time Lyman-a as well as continua. Only by the direct inclusion of Ly-a may we properly evaluate the effect of this strong line on the structure of the atmosphere. A new temperature-correction scheme was used. It is of the constraint type, is capable of handling very large opacity variations, and guarantees vanishingly small flux derivatives. The model atom assumed the upper fourteen levels in LTE, but permitted non-LTE deviations in the lower two levels. This model was suffi- cient to show that: (a) non-LTE effects from the continua cause a temperature rise at the surface; (b) this rise is partially offset by the inclusion of Ly-a, which causes a temperature drop, the non-LTE drop being very much smaller than the LTE; (c) Ly-a is so optically thick that it does not affect the formation of even the Lyman continuum; and (d) there is essentially no back-warming due to Ly-a in either the LTE case or the non-LTE case