Hercules X-1: Empirical Models of UV Emission Lines

Abstract

The UV emission lines of Hercules X-1, resolved with the HST GHRS and STIS, can be divided into broad (FWHM 750 km/s) and narrow (FWHM 150 km/s) components. The broad lines can be unambiguously identified with emission from an accretion disk which rotates prograde with the orbit. The narrow lines, previously identified with the X-ray illuminated atmosphere of the companion star, are blueshifted at both phi=0.2 and phi=0.8 and the line flux at phi=0.2 is 0.2 of the flux at phi=0.8. Line ratio diagnostics show that the density of the narrow line region is log n=13.4+/-0.2 and the temperature is T=1.0+/-0.2x10^5 K. The symmetry of the eclipse ingress suggests that the line emission on the surface of the disk is left-right symmetric relative to the orbit. Model fits to the O V, Si IV, and He II line profiles agree with this result, but fits to the N V lines suggest that the receding side of the disk is brighter. We note that there are narrow absorption components in the N V lines with blueshifts of 500 km/s.

arXiv commentTo be published in the Astrophysical Journal

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• The UV Spectrum of the Ultra-compact X-ray Binary- 4U 1627-673
• Discovery of mHz UV Quasiperiodic Oscillations in Hercules X-1
• RXTE Observations of Hercules X-1 During the July 1998 Short-high State
• Hot Outflowing Gas from the X-ray Binary Hercules X-1
• Atmospheric reflection during an anomalous low-state of Hercules X-1
• FUSE Observations of a Full Orbit of Hercules X-1: Signatures of Disk, Star, and Wind
• The ultraviolet colour of globular clusters in M31: a core density effect?
• Eclipsing Broad Emission Lines in Hercules X-1: Evidence for a Disk Wind?
• FUSE Observations of a Full Orbit of Scorpius X-1