Astrochemistry as a diagnostic of evolved stars in binary systems.

Low- and intermediate-mass stars disgorge their outer layers during the asymptotic giant branch (AGB) phase, one of the last stages of their lives. Material containing newly-formed elements and a variety of dust and molecules streams out of them in what we call a stellar wind. Studies resolving the extended circumstellar environments of AGB stars have revealed spirals, discs and bipolar outflows, with the shaping of the gas attributed to interactions with a companion. However, most of these companions are not directly observed, because their light is so strongly attenuated by the dust created around the AGB star. Astrochemistry is the study of molecules, dust and the chemical reactions that link them in astrophysical environments. I will discuss new methods that combine theoretical astrochemistry with observations to allow us to deduce the nature of the companion stars in binary systems with AGB stars. From this we can begin to understand how companion stars affect the length of the AGB phase.