Eclipsing broad emission lines in Hercules X-1: Evidence for a disk wind?

We present disk wind model calculations for the broad emission lines seen i n 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 redshifted to blueshif ted evolution of the line shape during the progression of the eclipse from ingress to egress that is indicative of disk emission. Furthermore, these l ines are single peaked, which implies that they may be formed in a disk win d similar to those we have proposed as producing the broad emission lines s een in the UV spectra of active galactic nuclei. We compute line profiles a s a function of eclipse phase and compare them to the observed line profile s. Various effects may modify the appearance of the lines including resonan t 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 obs erver's line of sight. The latter two effects can cause orbital and precess ional phase-dependent variations in the emission lines. Hence, examination of the line profiles as a function of these phases can, in principle, provi de additional information on the characteristics of the disk warp.