Subsonic structure of radiatively driven winds of early-type stars

Methods are developed for the calculation of extended nongray model atmospheres for early-type stars with radiatively driven mass loss. Models for a central star of a planetary nebula and a Wolf-Rayet star are calculated, and compared with hydrostatic model calculations. Scaling laws are given for explaining the differences and similarities of stars of different stellar mass. It is found that transonic flow cannot occur if only continuum sources of opacity are present, because a moderate outward increase of the flux mean opacity is required for a physically acceptable structure. Observations of the Of star zeta Pup and the Wolf-Rayet star HD 50896 are summarized that indicate the continuum formation regions are spatially extended