H2O masers in circumstellar envelopes

Abstract

The spatial structure of H2O maser emission at 22.235 GHz for 12-late-type variable stars has been measured with a resolution of 0.07 arcsec. The H2O 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 H2O 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 H2O 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.