THE QUASI-PERIODIC OSCILLATIONS OF VV PUPPIS

Four AM Her objects are known to exhibit low-amplitude, rapid quasi-periodic oscillations (QPOs) in their optical emission. Here, we present high-speed optical photometric observations of the QPO source VV Pup obtained during 1990 January. The observations were made in unfiltered light. We first confirm the results of Larsson (1989) that VV Pup is a strong source of QPOs and that the QPOs are confined to optical maximum showing that the QPOs are produced in or near the X-ray-producing shock formed as the accreting plasma merges onto the white dwarf. We then show that: (1) variations in the amplitudes of the QPOs over narrow bandwidths, deltanu approximately 0.1 Hz, around the peak of the QPOs, nu(QPO) approximately 0.6-0.7 Hz, are correlated. We also find a suggestion that the QPO powers at widely separated frequencies are also positively correlated. These results suggest that the QPOs are due to a broad-band process rather than to a narrow-band feature which wanders slowly in frequency space. (2) We isolate strong damped oscillations in several 81.92 s intervals. The pulse profiles are consistent with damped sinusoids. The strongest feature has an amplitude of several percent with frequency v approximately 0.64 Hz and quality Q approximately 21, or a coherence Of tau approximately 6.7. VV Pup is the third QPO source to show evidence of strong oscillations of moderate coherence.