How Do Massive Asymptotic Giant Branch Stars Lose All Their Mass?

Recent studies have made it increasingly clear that oxygen-rich and massive (>=5 M☉) asymptotic giant branch (AGB) stars go through only one, short, superwind. Although the superwind was originally introduced for the star to lose enough mass to reach that of a white dwarf, evidence is now building that the superwind lasts too short a time for it to be sufficiently efficient. The integrated mass lost during the whole superwind is not enough to remove the remaining H-rich envelope and terminate the AGB. Studies presented at the conference have shown, from methods based on both gas and dust, that the superwind lasts only ≲1200 years. The analysis of solid-state spectral bands of crystalline olivine (Mg2-2xFe2xSiO4) in the spectra of massive OH/IR stars is a powerful way to determine the extent of the superwind. De Vries, Blommaert, Waters et al. (2014) show that the temperature indicated by the observed 69mum band of crystalline olivine can only be reproduced by models with a geometrically compact superwind (RSW ≲ 2500 AU = 1400 R*). The way by which a star loses its remaining mass after the superwind is unknown. During the conference this problem was discussed and the most likely hypothesis would be a short but very strong phase after the superwind. This hyperwind would have a mass-loss rate of ≳10-3 M☉/yr