Chemistry on hot astrochemical dust surfaces: Sulfur in AGB outflows

Astrochemical models treat dust surfaces as ice covered. We investigate the effects of implementing increased bare dust binding energies of CO and S-bearing species on the chemistry in the outflows of asymptotic giant branch (AGB) stars. We demonstrate the potential for improving agreement with observations in the outflow of IK Tau.

Increasing the binding energies to measured and computationally derived values in high mass-loss AGB outflows increased the production of daughter species. Switching from a high binding energy on bare dust to weaker binding to ice, the gas phase abundance increased at a radius in agreement with observations of IK Tau, suggesting that displacement of bound species could contribute to this observational puzzle. Using a strong binding to bare dust, a gas phase increase was not observed, however parent species concentrations had to be increased by around a factor of four to explain observed concentrations.