1204.3173 (Noam Soker)

Merger by Migration at the Final Phase of Common Envelope Evolution    [PDF]

Noam Soker

I find the common envelope (CE) energy formalism, the CE \alpha-prescription, to be inadequate to predict the final orbital separation of the CE evolution in massive envelopes. I find that when the orbital separation decreases to ~10 times the final orbital separation predicted by the CE \alpha-prescription, the companion has not enough mass in its vicinity to carry away its angular momentum. The core-secondary binary system must get rid of its angular momentum by interacting with mass further out. The binary system interacts gravitationally with a rapidly-rotating flat envelope, in a situation that resembles planet-migration in protoplanetary disks. The envelope convection of the giant carries energy and angular momentum outward. The basic assumption of the CE \alpha-prescription, that the binary system gravitational energy goes to unbind the envelope, breaks-down. Based on that, I claim that merger is a common outcome of the CE evolution of AGB and red super-giants stars with an envelope to secondary mass ratio of M_{env}/M_2 >~5. I discuss some other puzzling observations that might be explained by the migration and merger processes.

View original: http://arxiv.org/abs/1204.3173