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Hercules X-1: Empirical Models of UV Emission Lines

B. Boroson·T. Kallman·S. Vrtilek·J. Raymond·M. Still·M. Bautista·H. Quaintrell
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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.

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B. Boroson, T. Kallman, S. Vrtilek, J. Raymond, M. Still, M. Bautista, H. Quaintrell. 1999-08-18. Hercules X-1: Empirical Models of UV Emission Lines. https://doi.org/10.1086/308272

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