The evolution of cataclysmic variable binary systems with circumbinary disks

The effect of a circumbinary (CB) disk on the evolution of a binary consisting of a low-mass secondary star with a white dwarf primary is investigated, taking into account the viscous spreading of matter within the circumbinary disk and the response of the secondary to mass loss. The CB disk is assumed to be fed a constant fraction δ of the mass transfer from the secondary to the primary through a wind such as those observed in nova-like: systems. The CB disk is effective in draining orbital angular momentum from the system provided that δ exceeds about 0.01. In this case, the mass transfer rates are elevated and the evolution accelerated in comparison with an evolution with the standard angular momentum loss processes of magnetic braking and gravitational radiation. The mass transfer rates for a given system can vary by more than an order of magnitude during its evolution. With a CB disk, a binary can thus evolve between the various subclasses of cataclysmic variables. A large spread in transfer rates at a given orbital period results, reflecting a range of ages of the systems, the possible presence of a CB disk already at the beginning of the evolution of the binary, and the mass and evolutionary state of the donor. For high mass input rates into the circumbinary disk (δ ≲ 0.015), the secondary can be completely dissolved in less than a Hubble time.