Models of X-ray photoionization in LMC X-4: Slices of a stellar wind

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 ht models to Goddard High Resolution Spectrograph (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 fitted by v proportional to (1 - 1/r)P, where beta is likely approximate to 1.4-1.6 and definitely less than 2.5. Escape probability models can fit the observed P Cygni profiles and provide measurements of the stellar wind parameters. The fits determine L-X/M = 2.6 +/- 0.1 x 10(43) ergs s(-1) M-circle dot(-1), yr, where L-X is the X-ray luminosity and M; 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.