Rapid oscillations in cataclysmic variables. I - The 71 second oscillation of DQ Herculis

Abstract

We present a new photometric study of the 71 s oscillation in the old nova DQ Herculis. All timings of the oscillation maxima may be phased with a simple ephemeris; the most likely choice has a large P term, which will, if continued, halt the speedup of the oscillation in approx.40 years.The oscillation shows a wealth of fascinating detail in its phase and amplitude variations around the binary orbit. We confirm the oscillation phase shift in eclipse found by Warner et al., and provide a more accurate description. We find that the pulses arrive systematically late by approx.6 s for a 1 hour interval around orbital phase 0.7. Multicolor observations establish that the visible oscillation arises from the reprocessing of the white dwarf's pulsed ultraviolet flux by the accretion disk.We also report new eclipse timings, and show that a sinusoidal modulation with a period of approx.14 years is present in all the timings sine 1954. This effect cannot be explained by the presence of a distant companion or by classical apsidal motion.