2007ApJ...667.1087B

We observed an entire 1.7 day orbit of the X-ray binary Hercules X-1 with the Far Ultraviolet Spectroscopic Explorer (FUSE). Changes in the O VI λλ1032, 1037 line profiles through eclipse ingress and egress indicate a Keplerian accretion disk spinning prograde with the orbit. These observations may show the first double-peaked accretion disk line profile to be seen in the Hercules X-1 system. Doppler tomograms of the emission lines show a bright spot offset from the Roche lobe of the companion star HZ Her, but no obvious signs of the accretion disk. Simulations show that the bright spot is too far offset from the Roche lobe to result from uneven X-ray heating of its surface. The absence of disk signatures in the tomogram can be reproduced in simulations including absorption from a stellar wind. We attempt to diagnose the state of the emitting gas from the C III λ977, C III λ1175, and N III λ991 emission lines. The latter may be enhanced through Bowen fluorescence.