Rapid oscillations in cataclysmic variables. XIII. WZ Sagittae revisited

We report new observations of the dwarf nova WZ Sagittae, showing the return of the 27.87 s oscillation in 1995/1996 high-speed optical light curves. As was true in 1978, the main peak of the power spectrum generally occurred at 27.87 or 25.96 s, with the signals sometimes simultaneously present. Weak transient signals were also seen at 28.20 and 29.69 s. An ASCA X-ray observation showed a significant peak at 27.86 +/- 0.01 s in the 2-6 keV band, which appeared to establish the star's membership as a "DQ Herculis star," in which accretion onto the white dwarf is channeled by a strong magnetic field. The X-ray period is most likely the true white dwarf spin period. However, we certainly do not understand the distribution of power among these various signals of slightly different period. This puzzling multiperiodic structure remains an impediment to full acceptance of WZ Sge as a DQ Her star The star's soft X-ray orbital light curve shows a strong but transient energy-dependent dip around orbital phase 0.7, which is probably due to absorption by an extended gas cloud in which the mass-transfer stream strikes the disk.