The infrared eclipse of V444 Cygni and the structure of Wolf-Rayet winds

The density structure of the wind of the WN5 component of V444 Cyg is modeled by combining infrared eclipse observations of the free-free continuum with previous optical work. The results show that the wind expands at a nearly constant velocity at large continuum optical depths, in contrast with present theories of O-star winds driven by radiation pressure in lines. For a schematic envelope with a density gradient proportional to some inverse power of radial distance and an optical depth in electron scattering, the acceptable models have exponents of approximately -1.5 to -2 and scattering optical depths of about 0.75 to 1.5, in good agreement with the model of the WN5 star HD 50896 constructed by Hartmann and Cassinelli (1977). A plane-parallel coronal model is definitely ruled out.