Fall back disks and the end of the common envelope phase

The common envelope interaction scenario was first proposed by Paczynski (1976) to explain the existence of cataclysmic variables. The interaction involves a binary system, where the more massive primary star extends its gas envelope as it becomes a giant, engulfing its companion. In this thesis we propose another mechanism to make up for the shortfall of previous studies, and investigate it via simulations. As previous simulations have found that most (≧ 60%) of the giant envelope is still bound to the system, our hypothesis is that the fall back of bound gas onto the binary system can lead to a further reduction of the orbital separation while unbinding more of the envelope gas. Our simulations show that the orbital separation is effectively reduced by a fall-back event. However, only a small amount of mass is unbound. We propose that a number of fall-back events are necessary (and likely inevitable) but that another energy source may be needed to fully unbind the envelope.