THE 4 PERIODICITIES OF THE CATACLYSMIC VARIABLE TV COLUMBAE

I present six nights of simultaneous optical photometry and spectroscopy aimed at observing the four periodicities of TV Col. The 32-min white dwarf spin period (known from the X-ray band) is not convincingly detected in the optical. The 5.5-h orbital period is manifest both photometrically and in the emission-line radial velocities. The emission lines show disc emission with a superimposed S-wave. Near orbital phase 0.8, the S-wave is at inferior conjunction, the photometric variation is at minimum, there is absorption in the line centres and we see X-ray dips. All these findings suggest that the rim of the disc is thickened at this location. The 4-d and 5.2-h cycles dominate the continuum variations but do not change the emission-line profiles. These modulations are not absolutely coherent. One photometric data set suggests that the optical eclipse (of the near part of the accretion disc only) has a depth independent of 4-d/5.2-h phase and source brightness. Other photometry is inconclusive owing to the shallowness of the eclipses and the small amplitude of the brightness variations. I discuss the origin of the extra modulations, concluding that they are probably caused by an accretion disc precessing with a 4-d retrograde cycle and interacting tidally with the secondary to produce the 5.2-h modulation. This phenomenon (possibly also occurring in TT Ari) has similarities to SU UMa stars in superoutburst, but the SU UMa mechanism cannot be applied directly to TV Col.