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

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.

56 pages, 12 figures, to be published in the Astrophysical Journal

References in corpus (2)

• Models of X-ray Photoionization in LMC X-4: Slices of a Stellar Wind
• Simultaneous HST/ASCA Observations of LMC X-4: X-ray Ionization Effects on a Stellar Wind

Cited by in corpus (13)

• The ephemeris, orbital decay, and masses of 10 eclipsing HMXBs
• The Discovery of Broad P Cygni X-ray Lines from Circinus X-1 with the Chandra High Energy Transmission Grating Spectrometer
• Stellar Wind Variations During the X-ray High and Low States of Cygnus X-1
• XMM-Newton X-ray spectroscopy of the high-mass X-ray binary 4U1700-37 at low flux
• Modelling the orbital modulation of ultraviolet resonance lines in high-mass X-ray binaries
• Stellar wind accretion and accretion disk formation: applications to neutron star high mass X-ray binaries
• The Evolution Of LMC X-4 Flares: Evidence For Super-Eddington Radiation Oozing Through Inhomogeneous Polar Cap Accretion Flows ?
• Spectroscopic Signatures of the Superorbital Period in the Neutron Star Binary LMC X-4
• High-mass X-ray binaries and OB-runaway stars
• Ultraviolet observations of the X-ray photoionized wind of Cygnus X-1 during X-ray soft/high state
• Models of X-ray Photoionization in LMC X-4: Slices of a Stellar Wind
• Testing Hydrodynamic Models of LMC X-4 with UV and X-ray Spectra
• Photoionized Lines in the X-ray Spectra of SMC X-1