557 Ghz observations of water vapor outflow from VY Canis Majoris and W Hydrae

We report the first detection of thermal water vapor emission in the 557 GHz, 1(10)-1(01) ground-state transition of ortho-H2O toward VY Canis Majoris. In observations obtained with the Submillimeter Wave Astronomy Satellite, we measured a flux of similar to450 Jy, in a spectrally resolved line centered on a velocity v(LSR) = 25 km s(-1) with an FWHM of similar to35 km s, somewhat dependent on the assumed line shape. We analyze the line shape in the context of three different radial outflow models for which we provide analytical expressions. We also detected a weaker 557 GHz emission line from W Hydrae. We find that these and other H2O emission-line strengths scale as suggested by Zubko and Elitzur.