Circumbinary Disks and Cataclysmic Variable Evolution

Abstract

The inÑuence of a circumbinary (CB) disk on the evolution of cataclysmic variable (CV) binary systems is investigated. We show that CB mass surface densities sufficient to inÑuence the evolution rate are plausibly provided by the outÑows observed in CVs, if the net e †ect of these winds is to deliver 10~4 to 10~3 of the mass transfer rate to the CB disk. The torque exerted by the CB disk provides a positive feedback between mass transfer rate and CB disk mass that can lead to mass transfer rates of D10~8 to 10~7 yr~1. This mechanism may be responsible for causing the range of variation of mass transfer M _ rates in CVs. In particular, it may explain rates inferred for the nova-like variables and the supersoft X-ray binary systems observed near the upper edge of the period gap (P D 3È4 hr), as well as the spread in mass transfer rates above and below the period gap. Consequences and the possible observability of such disks are discussed.