Late Stages of Stellar Evolution
The physics and chemistry of the circumstellar envelopes (CSEs) around evolved stars have much in common with the dense(r) ISM: in both areas, observations of the emission from molecules provide key information. We have investigated a range of interesting topics related to the chemistry of oxygen-rich and carbon-rich asymptotic giant branch stars. In particular, with ALMA and the VLA we have resolved their innermost regions and even resolved their photospheres. We started investigations of planetary nebulae in atomic fine structure and molecular lines with SOFIA and for the first time discovered the long-sought HeH+ ion in one of them. Stellar mergers represent an abrupt end of the evolution of two (or more) stars and the discovery of extraordinary chemical richness in one of them has opened a highly successful new line of research for us and astrochemistry in general. It has led to the discovery of 26 AlF, the first radioactive molecule found in an astronomical source. As an example, images, at different velocities of the extended atmosphere of the prototypical Mira variable, ο Ceti (Mira) are shown. Complex line profiles from vibrationally excited water have been detected probing infall and a sharp rise in the water abundance near the radio photosphere with temperatures in the range of 500-2000K.