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M. A. Wood, M. M. Montgomery (Florida Institute of Technology), J. C. Simpson (Computer Sciences Raytheon)
The superhump phenomenon observed in cataclysmic variable systems with mass ratios 0.03 < q < 0.33 is the result of a tidally-driven disk oscillation. Common (or ``positive'') superhumps are observed in disks undergoing high mass transfer rates during superoutburst or in some nova-like systems where the disk extends to the 3:1 eccentric inner Lindblad resonance. Numerical simulations show that over one oscillation period as viewed face-on, the tidal field pulls the disk into elongated shape, followed by relaxation back to a nearly circular shape. The axis of the positive superhump oscillation precesses slowly and progradely in the co-rotating frame, resulting in a superhump period slightly longer than the orbital period.
In recent years a handful of systems have been observed to show ``negative superhumps,'' in which the oscillation period is shorter than the orbital period. It has been suggested that nodal regression in a disk tilted with respect to the orbital plane could be the origin of the negative superhump phenomenon. The energy production curves we obtain from artificially tilted disks largely confirms this model, although some details of the observations remain unexplained.
The author(s) of this abstract have provided an email address for comments about the abstract: wood@astro.fit.edu