Pulsations and line profile changes in the ultraviolet spectrum of Hercules X-1: Results from a multiwavelength campaign

We report simultaneous X-ray and ultraviolet observations of the X-ray binary pulsar Hercules X-l, obtained over nearly half of a 1.7 day binary orbit using the ASCA X-ray telescope and the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope. The GHRS resolved, for the first time, two moving emission components. One feature in the N v lambda lambda 1238.8, 1242.8 doublet is broad (FWHM approximate to 1000 km s(-1)) and the other is narrow (FWHM approximate to 150 km s(-1)). We attribute the broad emission line to the X-ray-illuminated surface of a Keplerian accretion disk and the narrow line to the X-ray-heated atmosphere of the companion star, HZ Her. Near orbital phase phi(orb) = 0.80 (simultaneous with a pre-eclipse X-ray dip), the N v lambda 1242.8 component became stronger than the N v lambda 1238.8 component. Later in the orbit, the blue edge of the broad lines diminished as the approaching side of the accretion disk was occulted by HZ Her. UV continuum pulsations were detected for the first time, with an amplitude approximate to 0.5% of the steady flux. The pulse shapes of the UV continuum and hard X-rays were similar at phi(orb) = 0.83 but not at phi(orb) = 0.56. We found evidence for a stronger pulsation (amplitude approximate to 15%) within a narrow (0.25 Angstrom) segment of the broad 1242.8 Angstrom v component, only at phi(orb) = 0.80. We briefly discuss some implications of these observations for the gas hows in the Her X-l system.