X-RAY VARIABILITY IN V444 CYGNI - EVIDENCE FOR COLLIDING WINDS

Phase-resolved ROSAT observations of the soft X-ray flux from the W-R + O star binary V444 Cyg confirm the orbital dependence of the flux su ggested by Einstein IPC observations, showing a drop in flux around pr imary eclipse, when the W-R star is in front of the O star. The observ ed X-ray variability can be modeled as a wind eclipse of an X-ray sour ce by the Wolf-Rayet wind. If most of the X-rays from the system are p roduced in a region of shock-heated gas formed by the wind collision b etween the two stars, then the shocked gas has a large physical extent (r similar to 140R(WR)) if the observed variability is produced solel y by the eclipse of the region by the W-R wind. However, since the O s tar makes a significant contribution to the total X-ray flux from the system, the actual size of the shocked interaction region is probably much smaller. We discuss possible origins for the X-ray emission and c onclude that it is probable that at least a fraction of the observed X -ray emission comes from the wind collision.