Wolf-Rayet Stars. III. The Eclipsing System V444 Cygni

Photoelectric spectrum-scanner observations of the emission-line and continuum intensities have been obtained for the Woif-Rayet star V444 Cygni as a function of phase, with special concentration around secondary minimum so that the atmospheric stratification could be determined. Individual emission lines show greatly different eclipse curves decreasing in intensity at both secondary and primary minima. Secondary eclipse depths range from `-~8 per cent for He ii X4686 to `--30 per cent for N v X4609 at secondary minimum and from ~-25 per cent to `-~.-`5O per cent for the same lines at primary minimum. Interpretation of these eclipse data in terms of purely geometric effects proved to be impossible. The most likely reasons for this failure appear to arise from the following: (1) increased excitation by the o star of the side of the W-R envelope facing the 0 star and resulting asymmetrical light distribution; (2) optical thickness of the W-R envelope to many of the emission lines; (3) enlargement of effective size of the emitting region by electron scattering; and (4) completely individualistic behavior of emission lines without regard to ionization or excitation potential so that extremely selective excitation processes must be operative. Therefore no definite conclusion can be reached concerning the stratification struc- ture. The depth of secondary eclipse in continuum wavelengths increases with increasing wavelength and leads to a verification of the infrared excesses observed earlier in single W-R stars. It also implies that the presence of a hot star is not a necessary condition for the production of a W-R star, but does not rule out a much cooler companion for observed "single" W-R stars. The erratic fluctuations of both line and continuum intensities (as much as 0.1-mag increase in a 6- hour period) point to a random process of ejection, perhaps some type of large-scale prominence activity. Simple models such as uniform radial expansion are clearly ruled out