The mysterious nature of HS2331+3905
  We report the discovery of one unique cataclysmic variable drawn from the Hamburg Quasar Survey, HS2331+3905. Follow-up observations obtained over three years unveiled a very unusual picture. The large amplitude 3.5 h radial velocity variations obtained from our optical spectroscopy is not the orbital period of the system, as one would normally expect. Instead, extensive CCD photometry strongly suggests that HS2331+3905 is a short orbital period cataclysmic variable with Porb = 81.09 min, containing a cold white dwarf which appears to exhibit ZZ Ceti pulsations. 
S. Araujo-Betancor, B. T. Gaensicke, H. -J. Hagen, T. Marsh, J.   Thorstensen, E. Harlaftis, R. E. Fried, D. Engels