Vol. 546
In section 6. Interstellar and circumstellar matter

Evolved star water maser cloud size determined by star size

by A.M.S. Richards, S. Etoka, M.D. Gray, et al., A&A 546, A16

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One of the interesting uses of maser transitions is to define the kinematics of outflows, in particular those surrounding AGB and supergiant stars. The study by Richards et al. highlighted in this issue uses water maser images from MERLIN and monitoring from Pushchino to study the expanding envelope around a sample of supergiant and AGB stars over about a 5-year period. This shows clear evidence for acceleration and also a proportionality between the water cloud radius and the radius of the stellar photosphere.