We report the first detection of thermal water vapor emission in the 557 GHz , 1 _ { 10 } -1 _ { 01 } ground state transition of ortho-H _ { 2 } O toward VY Canis Majoris .
In observations obtained with the Submillimeter Wave Astronomy Satellite ( SWAS ) , we measured a flux of \sim 450 Jy , in a spectrally resolved line centered on a velocity v _ { LSR } = 25 km s ^ { -1 } with a full width half maximum of \sim 35 km s ^ { -1 } , 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 H _ { 2 } O emission line strengths scale as suggested by Zubko and Elitzur ( 2000 ) .