DQ Herculis in Profile: Whole Earth Telescope Observations and Smoothed Particle Hydrodynamics Simulations of an Edge-on Cataclysmic Variable System
Résumé
The old nova DQ Herculis was the Whole Earth Telescope Northern Hemisphere target for the 1997 July campaign and was observed on four nights with the SARA 0.9 m telescope during 2003 June. We present updated ephemerides for the eclipse and 71 s timings. The Fourier transform displays power at the presumed white dwarf spin period of 71.0655 s, but no significant power at either 142 or 35.5 s. The mean pulsed light curve is obtained by folding on the orbital period modulus the mean ephemeris of the 71 s period, and from this we calculate an O-C phase diagram and amplitude versus orbital phase diagrams. In addition to the phase variations during eclipse ingress and egress, the WET data reveal significant phase variations outside of eclipse. These must result from the self-eclipse of a nonaxisymmetric disk. We simulated the disk in DQ Her using smoothed particle hydrodynamics. We improve our effective spatial signal-to-noise ratio by combining 250 snapshots of the N=20,000 phase space solution over time to obtain a 5 million particle ensemble disk. From the surface shape of the ensemble disk, the radius and vertical height above the midplane of the rim of the reprocessing region can be derived as a function of azimuthal angle. From this profile we can calculate the O-C phase and amplitude diagrams as a function of inclination angle. The calculated O-C diagrams are a remarkably good match to the observed phase and amplitude variations of the 71 s signal. The best match is for inclination angle 89.7d.