Ultraviolet photometry from the Orbiting Astronomical Observatory XXXIX. The structure of the eclipsing Wolf-Rayet binary V444 Cygni as derived from light curves between 2460 A and 3.5 microns.

The structure of the expanding atmosphere and the physical characteristics of the WN5 component of V444 Cyg have been determined from an analysis of light curves for the wavelength range 2460 Å - 3.5 μm. The radius of the WN5 star's core is r₀ = 2.9 R_sun;; the temperature at its surface is ≡90,000K. A detailed analysis of the distribution of density, temperature and outflow velocity in the expanding atmosphere of this star is presented. The results agree best with the Beals model of Wolf-Rayet atmospheres in which the radial expansion is caused by a high radiation pressure gradient and the temperature structure is determined primarily by radiative transfer. The physical characteristics of the binary system and of the Wolf-Rayet component are consistent with theoretical predictions of the evolution of massive close binary systems with mass loss and mass exchange. The W-R component is in a post-main-sequence evolutionary stage, being a helium remnant formed as the result of case B mass exchange.