Radiation Field of Extended Stellar Atmospheres.

In this paper the problem of the radiation field in an extended atmosphere in which the transformation of ultraviolet radiation into Lyman-a radiation is taking place is considered. In treating this problem the Lyman-a contour is assumed to consist of a core and a wing with different absorption coefficients; also, account is taken of the ionization from the second quantum state. It is shown that both these effects reduce the transformation into Lyman-a to an extent that the pressure resulting from the radiation is comparable to that due to the ultraviolet radiation. However, it appears that in the outermost parts of the nebula radiation pressure due to Lyman-a may be one hundred times that of the ultraviolet radiation. For planetary nebulae the main effect comes from the contour's not being strictly rectangular, while in the atmospheres of Be stars the ionization from the second quantum state is the principal factor. The two effects are comparable when the dilution factor is about 0.0016.