Stars ascending the red giant branch for the second time, asymptotic giant branch (AGB) stars, lose considerable amounts of matter in a slow stellar wind. The wind is so intense that it is this process that limits the lifetimes of stars on the AGB, and for many of them determines their final fate. A large fraction of all stars in a galaxy is believed to go through this evolutionary phase. The mechanism(s) behind the mass loss is not yet identified with certainty, but the regular pulsations of the star and the formation of microscopic dust particles in its atmosphere are believed to play a major role. The mass loss leads to the formation of a circumstellar envelope (CSE) of gas and dust, that plays a major role in the formation of planetary nebulae (PNe), and also returns, in the star processed, material to the interstellar medium.
The research at Stockholm Observatory centres on the dependence of the mass loss characteristics on the stellar properties, the large-scale geometry and kinematics of the CSEs, the detailed structure of the circumstellar medium, the chemistry of the CSEs, and the shaping of the PNe due to the interaction of a fast post-AGB wind and the CSE.