Time Resolved Ultraviolet Spectroscopy of DQ Herculis: Eclipses and   Pulsations
  The magnetic cataclysmic variable DQ Herculis was observed with the Faint Object Spectrograph onboard the Hubble Space Telescope (HST) over four consecutive satellite orbits, including the first observation in the UV of DQ Her through eclipse minimum. Strong emission in N V, C IV, Si IV, and He II and weak emission in O I, S III, Ni II, N IV, Si III, and C III was seen. Time resolved spectroscopy was obtained over 3 orbits with the G160L grating. At the eclipse minimum, the UV continuum was completely eclipsed for < 5% of the orbital period. This implies that the UV continuum emission region is very compact. By contrast, none of the emission lines were completely eclipsed, most notably C IV which dropped by only ~75%. DQ Her is known to have intermittent pulsations in the optical and UV at a period of 71 s, due to the rotation of the accreting white dwarf. As in our previous observations, the UV continuum and the C IV emission show sporadic 71 s pulsations. The mechanism(s) which determine the pulsation amplitudes are clearly complex. The strong emission lines and continuum were auto-correlated during the first and third HST orbits and all show a variability timescale of ~160 s. The intensities of these lines were also cross-correlated with the continuum and show a strong correlation with the continuum with a timelag of < 4 s. The data during the fourth HST orbit were collected with the G190H grating (1600-2350 Angstroms with 1.5 Angstrom spectral resolution) in standard spectroscopy mode (240 s time resolution). These observations resolve He II 1640 into a broad (1,400 km/s), asymmetric line. 
Andrew D. Silber, Scott F. Anderson, Bruce Margon (University of   Washington) and Ronald A. Downes (STScI)