Dwarf Nova Oscillations and Quasi-Periodic Oscillations in Cataclysmic Variables, IV. Observations of Frequency Doubling and Tripling in VW Hyi

Abstract

We present new observations of the rapid oscillations in the dwarf nova VW Hyi, made late in outburst. These dwarf nova oscillations (DNOs) increase in period until they reach 33 s, when a transition to a strong 1st harmonic and weak fundamental takes place. After further period increase the 2nd harmonic appears; often all three components are present simultaneously. This 1:2:3 frequency suite is similar to what has been seen in some neutron star and black hole X-Ray binaries, but has not previously been seen in a cataclysmic variable. When studied in detail the fundamental and 2nd harmonic vary similarly in phase, but the 1st harmonic behaves independently, though keeping close to twice the frequency of the fundamental. The fundamental period of the DNOs, as directly observed or inferred from the harmonics, increases to ~100 s before the oscillation disappears as the star reaches quiescence. Its maximum period is close to that of the `longer period' DNOs observed in VW Hyi. The quasi-periodic oscillations (QPOs), which have fundamental periods 400 -- 1000 s, behave in the same way, showing 1st and 2nd harmonics at approximately the same times as the DNOs. We explore some possible models. One in which the existence of the 1st harmonic is due to transition from viewing a single accretion region to viewing two regions, and the rate of accretion onto the primary is modulated at the frequency of the 1st harmonic, as in the `beat frequency model', can generate the suite of DNO frequencies observed. But the behaviour of the QPOs is not yet understood.

16 pages, 13 figures; accepted for publication in MNRAS

References in corpus (5)

• High- and low-frequency quasi-periodic oscillations in the X-ray light curves of the black hole transient H1743-322
• Far Ultraviolet Observations of the Dwarf Novae SS Aur and RU Peg in Quiescence
• QPOs in Cataclysmic Variables and in X-ray Binaries
• Composite Accretion Disk and White Dwarf Photosphere Analyses of the FUSE and HST Observations of EY Cygni
• An HST STIS Observation of VW Hydri at the Exact FUV Onset of an Outburst

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• High speed photometry of faint cataclysmic variables - VI. Car2, V1040 Cen, Ha 075648, IL Nor (Nova Nor 1893), HS Pup (Nova Pup 1963), SDSS J2048-06, CSS 081419-005022 and CSS 112634-100210
• The Interpretations For the Low and High Frequency QPO Correlations of X-ray Sources Among White Dwarfs, Neutron Stars and Black Holes
• Dwarf Nova Oscillations and Quasi-Periodic Oscillations in Cataclysmic Variables - VIII. VW Hyi in outburst observed with the Southern African Large Telescope
• New Ultraviolet Observations of AM CVn
• Wavelets with Ridges: A High-Resolution Representation of Cataclysmic Variable Time-Series
• Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables - VII. OY Carinae and oscillations in dwarf novae in quiescence
• Disc-Magnetosphere interactions in Cataclysmic Variable Stars
• Long-term photometric behavior of the eclipsing cataclysmic variable V729 Sgr