Hydrodynamic Simulations of the Interaction between an AGB Star and a Main Sequence Companion in Eccentric Orbits

TL;DR

This study uses hydrodynamic simulations to explore how eccentric binary interactions involving an AGB star can lead to common envelope phases and mergers, explaining features of the Rotten Egg Nebula.

Contribution

It provides new insights into the binary interaction processes and the formation of the nebula through detailed simulations and analytical estimates of jet properties.

Findings

Roche lobe overflow occurs only for periods much less than 100 years.

Mass transfer leads to a common envelope phase within several orbits.

Jets similar to those observed can be produced by super-Eddington accretion in the simulated scenarios.

Abstract

The Rotten Egg Nebula has at its core a binary composed of a Mira star and an A-type companion at a separation >10 au. It has been hypothesized to have formed by strong binary interactions between the Mira and a companion in an eccentric orbit during periastron passage ~800 years ago. We have performed hydrodynamic simulations of an asymptotic giant branch star interacting with companions with a range of masses in orbits with a range of initial eccentricities and periastron separations. For reasonable values of the eccentricity, we find that Roche lobe overflow can take place only if the periods are <<100 years. Moreover, mass transfer causes the system to enter a common envelope phase within several orbits. Since the central star of the Rotten Egg nebula is an AGB star, we conclude that such a common envelope phase must have lead to a merger, so the observed companion must have been a tertiary companion of a binary that merged at the time of nebula ejection. Based on the mass and timescale of the simulated disc formed around the companion before the common envelope phase, we analytically estimate the properties of jets that could be launched. Allowing for super-Eddington accretion rates, we find that jets similar to those observed are plausible, provided that the putative lost companion was relatively massive.