Abstract
We review the recent development of observations of molecules in circumstellar envelopes of evolved stars. The large collecting areas and high spatial resolution of newly constructed radio telescopes have provided a resurgence of research in this area. Many molecules bearing silicon atoms, and heavier metals have been found. Observations with a spatial resolution of a few arcseconds have become possible by millimeter wave interferometers, giving us detailed information on the structure of the circumstellar envelopes. Especially bipolar and spherical flows in stars with large mass loss rates have been extensively mapped in various molecular lines. It has been recognized that molecular abundances are affected by ion-molecule reactions in the outer envelope. The theoretical evolutionary tracks from red giants to planetary nebulae have been confirmed further by detecting stars in a transition phase between oxygen- and carbon-rich atmospheres.
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