| Evolved stars are important sources of matter into the interstellar medium because of their dense outflows. These outflows are variable on many timescales and their physics and chemistry are not well understood. We propose to use the unique capabilities of the HERSCHEL Space Observatory to study the role of water in the stellar winds of oxygen-rich Asymptotic Giant Branch (AGB) stars with unprecedented detail. HERSCHEL will for the first time give a full inventory of water both in the gas phase and in the form of solid water ice. Water plays a pivotal role in the physics and chemistry of the molecular envelopes that surround AGB stars. The formation, destruction, as well as the importance of water for heating and cooling of molecular gas will be studied in stars with a wide range in stellar wind properties. We will combine the water analysis with that of the simpler molecule CO and with the thermal emission from the solid material that condenses in the wind to find the chemical, thermal and kinematical structure of oxygen-rich AGB winds, and to determine their mass-loss history. |
