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Models of X-ray Photoionization in LMC X-4: Slices of a Stellar Wind

B. Boroson·T. Kallman·R. McCray·S. D. Vrtilek·J. Raymond
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Abstract

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.

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B. Boroson, T. Kallman, R. McCray, S. D. Vrtilek, J. Raymond. 1998-11-17. Models of X-ray Photoionization in LMC X-4: Slices of a Stellar Wind. https://doi.org/10.1086/307336

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