  We show that the orbital variation in the UV P Cygni lines of the X-ray
binary LMC X-4 results when X-rays photoionize nearly the entire region outside
of the X-ray shadow of the normal star. We fit models to HST GHRS observations
of N V and C IV P Cygni line profiles. Analytic methods assuming a spherically
symmetric wind show that the wind velocity law is well-fit by v~(1-1/r)^beta,
where beta is likely 1.4-1.6 and definitely <2.5. Escape probability models can
fit the observed P Cygni profiles, and provide measurements of the stellar wind
parameters. The fits determine Lx/Mdot=2.6+/-0.1 x10^43 erg/s/Msun yr, where Lx
is the X-ray luminosity and Mdot is the mass-loss rate of the star. Allowing an
inhomogeneous wind improves the fits. IUE spectra show greater P Cygni
absorption during the second half of the orbit than during the first. We
discuss possible causes of this effect.
