Mass loss from stars is fundamental to the chemical evolution of galaxies. During the late stages of stellar evolution, asymptotic giant branch (AGB) stars are usually surrounded by a thick shell of dust. The dust has important astrophysical impacts, including: a strong acceleration in the outflow velocity, propelled by absorption of stellar radiation; provision of surfaces for heterogeneous chemical synthesis in the interstellar medium; and planetary formation around young stars. The dust around oxygen-rich AGB stars is largely composed of Mg-Fe silicates, but how these silicates actually form in this environment of high temperatures (&gt;1200 K), low pressures (&lt; 0.1 μbar) and chemically reducing conditions (the major species are H and H2) remains an important unsolved problem. In this presentation I will examine two aspects of dust formation: 1) the formation of highly refractory alumina (Al2O3) and perovskite (CaTiO3) nanoparticles, which can act as nucleation seeds on which the major metal silicates can condense in the cooler part of the outflow; 2) the role of vibrational disequilibrium in facilitating dust formation. Vibrational disequilibrium, where molecules have a significantly lower vibrational temperature than their kinetic (translational) temperature because optical emission is faster than collisional energy transfer, opens up dust formation pathways which involve relatively unstable intermediates.

Silicate dust formation in stellar outflows

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.