Eclipsing Broad Emission Lines in Hercules X-1: Evidence for a Disk Wind?

Abstract

We present disk wind model calculations for the broad emission lines seen in the ultraviolet spectra of the X-ray binary Hercules X-1. Recent HST/STIS observations of these lines suggest that they are kinematically linked to the orbital motion of the neutron star and exhibit a red-shifted to blue-shifted evolution of the line shape during the progression of the eclipse from ingress to egress which is indicative of disk emission. Furthermore, these lines are single-peaked which implies that they may be formed in a disk wind similar to those we have proposed as producing the broad emission lines seen in the UV spectra of active galactic nuclei. We compute line profiles as a function of eclipse phase and compare them to the observed line profiles. Various effects may modify the appearance of the lines including resonant scattering in the wind itself, self-shadowing of the warped disk from the central continuum, and self-obscuration of parts of the disk along the observer's line-of-sight. These latter two effects can cause orbital and precessional phase dependent variations in the emission lines. Hence, examination of the line profiles as a function of these phases can, in principle, provide additional information on the characteristics of the disk warp.

32 pages, 9 figures, LaTeX, Accepted for publication in ApJ

References in corpus (6)

• Warped accretion discs and the long periods in X-ray binaries
• Radiation driven winds from luminous accretion disks
• Radiation-Driven Warping: The Origin of Warps and Precession in Accretion Disks
• The 35-Day Evolution of the Hercules X-1 Pulse Profile: Evidence For A Resolved Inner Disk Occultation of the Neutron Star
• The Origin of Warped, Precessing Disks in X-Ray Binaries
• Hercules X-1: Empirical Models of UV Emission Lines

Cited by in corpus (8)

• Variability of the X-ray P Cygni Line Profiles from Circinus X-1 Near Zero Phase
• High-Resolution X-ray Spectroscopy of Hercules X-1 with the XMM-Newton RGS: CNO Element Abundance Measurements and Density Diagnostics of a Photoionized Plasma
• Identification of an Extended Accretion Disk Corona in the Hercules X-1 Low State: Moderate Optical Depth, Precise Density Determination, and Verification of CNO Abundances
• A Wind Driven Warping Instability in Accretion Disks
• The UV Spectrum of the Ultra-compact X-ray Binary- 4U 1627-673
• Hot Outflowing Gas from the X-ray Binary Hercules X-1
• FUSE Observations of a Full Orbit of Hercules X-1: Signatures of Disk, Star, and Wind
• FUSE Observations of a Full Orbit of Scorpius X-1