出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We have monitored cm-wave masers in circumstellar envelopes using MERLIN and VLBI. These images resolve the AU-scale structure and kinematics of the winds and reveal how cloud sizes and incipient asymmetries appear to depend on the stellar masses and magnetic fields. The water maser monitoring data also allows us to differentiate between models for matter-bounded and amplification-bounded masers. We find that the clouds in most sources are on average spherical, but flattened emission regions are present in some Miras which also show other evidence for the presence of shocks. The water maser clouds are found to be denser than their surroundings, but the exponential nature of maser amplification has hitherto made it very hard to reconstruct precise physical conditions. We look ahead to the opportunities to remedy this problem provided by EVN developments, the EVLA, e-MERLIN and in particular Early Science with ALMA.
