A Model for the Formation of Large Circumbinary Disks Around Post AGB Stars

TL;DR

This paper presents a model explaining the formation of large circumbinary disks around post-AGB stars through jet-driven back-flow of slow stellar wind material, supported by 2D simulations.

Contribution

It introduces a new mechanism for disk formation involving jet-induced back-flow, supported by numerical simulations, and suggests the role of non-axisymmetric jets in angular momentum transfer.

Findings

Jets create vortex flows that push slow wind material inward.

Up to 0.001 solar masses of material can back-flow to the center.

The model links jet activity to disk formation around post-AGB binaries.

Abstract

We propose that the large, radius of ~1000 AU, circumbinary rotating disks observed around some post-asymptotic giant branch (post-AGB) binary stars are formed from slow AGB wind material that is pushed back to the center of the nebula by wide jets. We perform 2D-axisymmetrical numerical simulations of fast and wide jets that interact with the previously ejected slow AGB wind. In each system there are two oppositely launched jets, but we use the symmetry of the problem and simulate only one jet. A large circularization-flow (vortex) is formed to the side of the jet which together with the thermal pressure of the shocked jet material accelerate cold slow-wind gas back to the center from distances of ~1000-10000 AU. We find for the parameters we use that up to 0.001 Mo is back-flowing to the center. We conjecture that the orbital angular momentum of the disk material results from the non-axisymmetric structure of jets launched by an orbiting companion. This conjecture will have to be tested with 3D numerical codes.