Merger by migration at the final phase of common envelope evolution

Noam Soker*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


I find the common envelope (CE) energy formalism, the CE α-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 α-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 α-prescription, that the binary system's 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.

Original languageEnglish
Pages (from-to)18-22
Number of pages5
JournalNew Astronomy
Issue number1
StatePublished - Jan 2013
Externally publishedYes


  • AGB and post-AGB
  • Binaries: close
  • Supernovae: general
  • White dwarfs

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