Low-mass binary-induced outflows from asymptotic giant branch stars

Abstract

A significant fraction of planetary nebulae (PNe) and protoplanetary nebulae (PPNe) exhibit aspherical, axisymmetric structures, many of which are highly collimated. The origin of these structures is not entirely understood, however, recent evidence suggests that many observed PNe harbour binary systems, which may play a role in their shaping. In an effort to understand how binaries may produce such asymmetries, we study the effect of low-mass (<0.3 M⊙) companions (planets, brown dwarfs and low-mass main-sequence stars) embedded into the envelope of a 3.0-M⊙ star during three epochs of its evolution [red giant branch, asymptotic giant branch (AGB), interpulse AGB]. We find that common envelope evolution can lead to three qualitatively different consequences: (i) direct ejection of envelope material resulting in a predominately equatorial outflow, (ii) spin-up of the envelope resulting in the possibility of powering an explosive dynamo-driven jet and (iii) tidal shredding of the companion into a disc which facilitates a disc-driven jet. We study how these features depend on the secondary's mass and discuss observational consequences.