SPH modelling of wind-companion interactions in eccentric AGB binary systems

TL;DR

This study uses 3D SPH simulations to explore how wind-companion interactions in eccentric AGB binary systems influence wind morphology, revealing the formation of regular spirals, bow-shocks, and equatorial enhancements depending on wind velocity and eccentricity.

Contribution

It provides new insights into the formation of complex wind structures in eccentric AGB binaries through high-resolution simulations, highlighting the effects of wind velocity and orbital eccentricity.

Findings

High wind velocity leads to regular, flattened spiral structures.

Lower wind velocity results in irregular morphologies with bow-shocks.

Eccentricity causes phase-dependent, complex wind interactions and equatorial density enhancements.

Abstract

The late evolutionary stages of low- and intermediate-mass stars are characterised by mass loss through a dust-driven stellar wind. Recent observations reveal complex structures within these winds, that are believed to be formed primarily via interaction with a companion. How these complexities arise, and which structures are formed in which type of systems, is still poorly understood. Particularly, there is a lack of studies investigating the structure formation in eccentric systems. We aim to improve our understanding of the wind morphology of eccentric AGB binary systems by investigating the mechanism responsible for the different small-scale structures and global morphologies that arise in a polytropic wind with different velocities. Using the smoothed particle hydrodynamics (SPH) code Phantom, we generate nine different high-resolution, 3D simulations of an AGB star with a solar-mass companion with various wind velocity and eccentricity combinations. The models assume a polytropic gas, with no additional cooling. We conclude that for models with a high wind velocity, the short interaction with the companion results in a regular spiral morphology, that is flattened. In the case of a lower wind velocity, the stronger interaction results in the formation of a high-energy region and bow-shock structure that can shape the wind into an irregular morphology if instabilities arise. High-eccentricity models show a complex, phase-dependent interaction leading to wind structures that are irregular in three dimensions. However, the significant interaction with the companion compresses matter into an equatorial density enhancement, irrespective of eccentricity.