Abstract
The spatial structure of H/sub 2/O maser emission at 22.235 GHz for 12-late-type variable stars has been measured with a resolution of 0.07 arcsec. The H/sub 2/O maser regions of Mira variables range from 9 or less to 108 AU in total extent, while those of supergiant long-period variables are 300-720 AU in extent. The size of the H/sub 2/O maser regions of giants and supergiants is correlated with the stellar mass-loss rate. Several of the observed sources show evidence for nonspherical geometry in the distribution of their H/sub 2/O maser emission. The Mira variable IK Tau exhibits about 31 maser features over a total velocity range of 41 km/s. The spatial distribution of these features appears to be consistent with two spherical shells of radii 25 and 59 AU, both expanding at a velocity of 15.5 km/sec from the star. Evidence is found for density inhomogeneities and turbulent motions in the envelopes of both IK Tau and R Aql. 34 references.
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