Energizing the last phase of common-envelope removal

Abstract

We propose a scenario where a companion that is about to exit a common envelope evolution (CEE) with a giant star accretes mass from the remaining envelope outside its deep orbit and launches jets that facilitate the removal of the remaining envelope. The jets that the accretion disk launches collide with the envelope and form hot bubbles that energize the envelope. Due to gravitational interaction with the envelope, that might reside in a circumbinary disk, the companion migrates further in, but the inner boundary of the circumbinary disk continues to feed the accretion disk. While near the equatorial plane mass leaves the system at a very low velocity, along the polar directions velocities are very high. When the primary is an asymptotic giant branch star, this type of flow forms a bipolar nebula with very narrow waists. We compare this envelope removal process with four others last-phase common envelope removal processes. We also note that the accreted gas from the envelope outside the orbit in the last-phase of the CEE might carry with it angular momentum that is antialigned to the orbital angular momentum. We discuss the implications to the possibly antialigned spins of the merging black hole event GW170104.