Floquet analysis of disk instabilities and superhumps in Cataclysmic Variables

We analyze the dynamical stability of hydrodynamical flows in the equatorial plane of a thin axisymmetric accretion disk in close binary systems. The periodic tidal forces of the companion star induce parametric instabilities, which are characterized by the Floquet exponent. We propose that the onset of superhumps can be understood in this context. Comparing our model with well-known systems leads to the conjecture that the onset of superhumps is due to the coupling between the fluid’s velocity field and the enthalpy fluctuations which generates pressure fluctuations. We also discuss superhumps in some particular systems belonging to the class of old novae or nova-like systems and the controversial case of TV Col.