We present our past and current long-term monitoring program of water masers in the circumstellar envelopes of evolved stars, augmented by occasional interferometric observations. Using as example the Mira-variable U Her, we identify three types of variability: periodic (following the optical variation), long-term (years-decades) and short-term irregular (weeks-months). We show there are regions in the maser shell where excitation conditions are favourable, which remain stable for many years. Lifetimes of maser clouds in the wind-acceleration zone are of the order of up to a few years. Much longer lifetimes are found for the peculiar case of a maser cloud outside that zone (as in RT Vir), or in some cases where the motion of spectral features can be followed for the entire 2 decade monitoring period (as in red supergiant VX Sgr).

We present interferometric continuum and molecular line emission maps obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of OH231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (AGB) star that is key to understand the remarkable changes in nebular morphology and kinematics during the short transition from the AGB to the Planetary Nebula (PN) phase. The excellent angular resolution of our maps (∼20 mas ∼30 AU) allows us to scrutinize the central nebular regions of OH231.8+4.2, which hold the clues to understanding how this iconic object assembled its complex nebular architecture. We report, for the first time in this object and others of its kind (i.e. pre-PNe with massive bipolar outflows), the discovery of a rotating circumbinary disk of radius ∼30 AU traced by NaCl, KCl, and H2O emission lines. The disk lies at the base of a young bipolar wind with signs of rotation as well. A compact spatially resolved dust disk is found perpendicular to the bipolar outflow. We also identify a point-like continuum source, which likely represents the central Mira star enshrouded by a ∼3 R* shell or disk of hot (∼1400 K) freshly formed dust. The point source is slightly off-centre from the disk centroid, enabling us for the first time to place constraints to the orbital separation of the central binary system.

Low- and intermediate-mass stars experience a phase of carbon enrichment and slow neutron-capture nucleosynthesis (s-process) on the asymptotic giant branch. An interesting element is the radioactive technetium, whose presence is a clear indication that nucleosynthesis happened recently. Analysing the element abundances not only in the hot evolved stars at the center of planetary nebulae helps to derive constraints for the evolution of these stars. Doing so also in their companions if they are in a binary, provides information on the mass-transfer history.

We carefully consider numerous explanations for the sulfur abundance anomaly in planetary nebulae. No one rationale appears to be satisfactory, and we suggest that the ultimate explanation is likely to be a heretofore unidentified feature of the nebular gas which significantly impacts the sulfur ionization correction factor.