Comments on the final orbital separation in common envelope evolution

Noam Soker*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

I study some aspects of common envelope evolution, where a compact star enters the envelope of a giant star. I show that in some binary systems under a narrow range of parameters, a substantial fraction of the giant stellar envelope is lost before the onset of the common envelope. The reduced envelope mass at the onset of the common envelope implies that the binary system emerges from the common envelope with a relatively large orbital separation. I therefore caution against a simple treatment, which omits this process, in the study of systems that evolved through a common envelope phase and ended with a relatively large orbital separation, e.g. PG1115+166. A fraction of the envelope that is lost while the companion is still outside the giant stellar envelope is accreted by the companion. The companion may form an accretion disc and blow two jets. I propose this scenario for the formation of the bipolar planetary nebula NGC 2346, which has a binary nucleus with an orbital period longer than that of any other known binary system in planetary nebulae. These conclusions are based on an analytical study, which ignores some processes, e.g. mass accretion by the companion, and the time evolution of the giant stellar radius - in particular because of a thermal pulse. More accurate numerical calculations should validate these results, as well as examine the requirements on the time evolution of the radius of the giant for such a scenario to occur. Because this scenario, of a late common envelope phase, occurs for a narrow range of parameters, I expect it to be applicable to a small, but non-negligible, number of systems.

Original languageEnglish
Pages (from-to)1229-1233
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society
Volume336
Issue number4
DOIs
StatePublished - 11 Nov 2002
Externally publishedYes

Keywords

  • Binaries: general
  • Stars: AGB and post-AGB
  • Stars: evolution
  • Stars: mass-loss

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