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

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. Subject headings: hydrodynamics – planetary nebulae