The Formation of Crystalline Dust in AGB Winds from Binary Induced Spiral Shocks

TL;DR

This paper proposes that binary companions influence the shaping of AGB star winds, creating spiral shocks that facilitate the formation of crystalline dust from amorphous grains in the wind's orbital plane.

Contribution

It introduces a mechanism where binary-induced spiral shocks in AGB winds promote crystalline dust formation, explaining observed dust structures in planetary nebulae.

Findings

Binary companions induce spiral shocks in stellar winds.

Spiral shocks lead to annealing of amorphous dust into crystalline form.

Crystalline dust formation is likely in the orbital plane of binary systems.

Abstract

As stars evolve along the Asymptotic Giant Branch, strong winds are driven from the outer envelope. These winds form a shell, which may ultimately become a planetary nebula. Many planetary nebulae are highly asymmetric, hinting at the presence of a binary companion. Some post-Asymptotic Giant Branch objects are surrounded by torii of crystalline dust, but there is no generally accepted mechanism for annealing the amorphous grains in the wind to crystals. In this Letter, we show that the shaping of the wind by a binary companion is likely to lead to the formation of crystalline dust in the orbital plane of the binary.