The Wolf‐Rayet Binary V444 Cygni Under the Spectroscopic Microscope. II. Physical Parameters of the Wolf‐Rayet Wind and the Zone of Wind Collision

New, extensive, high signal-to-noise, phase-dependent optical spectroscopy, along with simultaneous narrowband continuum photometry, leads to restrictions on the electron temperature and density in the wind close to the Wolf-Rayet component of the eclipsing binary V444 Cygni (WN5 + O6 V-III). Detailed study of the phase dependence of the equivalent widths and line profiles of the W-R star reveals significant ionization stratification in the W-R wind. Our previous discussion of the wind-wind collision effects on He I lines is extended to He II lines. We find that (1) the wind-wind collision zone is detached from the surface of the O star; (2) the radiation field of the O star does not inhibit the initial acceleration of the W-R wind; however, it does brake the flow just prior to entrance into the collision zone; (3) the shocked gas experiences rapid, t cool ≲ (2-4) × 10 4 s, and profound cooling via radiative losses, leading to high compression of the postshock gas.