DR. LUKE CHAMANDY

A large percentage of stars exist in binary systems. When one star evolves it can expand to fill its Roche lobe and mass transfer to the companion ensues. If the companion is unable to accrete all of this mass then it will overflow its own Roche lobe, leading to a common envelope surrounding the companion and core of the giant. The core and companion will spiral together owing to gas dynamical friction. This common envelope evolution is believed to be a critical process in the progenitors of many phenomena, including bipolar planetary nebulae, compact object mergers, and type Ia supernovae. However, it is difficult to model or simulate because of the inherent 3D structure and large dynamical range in both length and time. Numerical studies have yet to conclusively determine how the envelope ejects and a tight binary results, if only the binary potential energy is used to propel the envelope. Additional power sources might be necessary and accretion onto the inspiraling companion is one such source. Here we use high resolution global 3D hydrodynamic simulations of common envelope evolution with the adaptive mesh refinement code AstroBEAR to bracket the range of companion accretion rates by comparing runs that remove mass and pressure via a subgrid accretion model with those that do not. The results show that if a pressure release valve is available, super-Eddington accretion may be common. Jets are a plausible release valve in these environments, and they could also help unbind and shape the envelopes.