1995PASP..107..657P

We have acquired 190 hours of high-speed photometry of the cataclysmic variable which is the probable optical counterpart of the hard X-ray source H 0551-819. An optical modulation at P = 2.9518 hr was always present, and probably represents the underlying orbital period of the binary. In January 1995, no other period was obvious, but there was evidence for a signal of low coherence at P = 2.88 hr.

During the interval December 1993-February 1994, the star displayed a much richer spectrum of periodic behavior. Aside from the orbital signal, there were also strong signals at suggest two kinds of "superhumps" in the star, possibly arising from apsidal and nodal precession of the accretion disk.

Finally, the power spectrum at high frequency revealed oscillations with a period in the range 17-22 min; close study of the peaks showed evidence for underlying stable signals at P = 1040.4, 1293.4, and 1707.6 s. These probably arise from the rapid rotation of the accreting white dwarf, with sidebands produced by reflection effects in the binary. The likely white dwarf spin period is either 1040.4 or 2080.8 s.