The Interaction of Stellar Objects within a Common Envelope

We use high-resolution, three-dimensional hydrodynamics simulations to study the hydrodynamic and gravitational interaction between stellar companions embedded within a differentially rotating common envelope. Specifically, we evaluate the contributions of the non-axisymmetric gravitational tides and pressure forces to the drag force and, hence, to the dissipation rate and the mass accumulated onto the stellar companion. We find that the gravitational drag dominates the hydrodynamic drag during the spiral in phase, leading to the result that a simple prescription based on a gravitational capture radius formalism significantly underestimates the dissipation rate and overestimates the spiral in decay timescale. Although the rate of mass accretion fluctuates significantly, we observe a secular trend leading to an effective rate of mass accretion which is significantly less than the rate based on a gravitational capture radius. The implications of these results are discussed within the context of accretion of compact objects in the common envelope phase. Subject headings: binaries: close – hydrodynamics – stars: evolution