Interferometric Observation of the Highly Polarized SiO Maser Emission from thev= 1,J= 5-4 Transition Associated with VY Canis Majoris

We used the Submillimeter Array to image the SiO maser emission in the $v=1$,\$J=5-4$ transition associated with the peculiar red supergiant VY CanisMajoris. We identified seven maser components and measured their relativepositions and linear polarization properties. Five of the maser components arecoincident to within about 150 mas ($\sim$ 200 AU at the distance of 1.5 kpc);most of them may originate in the circumstellar envelope at a radius of about50 mas from the star along with the SiO masers in the lowest rotationaltransitions. Our measurements show that two of the maser components may beoffset from the inner stellar envelope (at the 3$\sigma$ level of significance)and may be part of a larger bipolar outflow associated with VY CMa identifiedby Shinnaga et al. The strongest maser feature at a velocity of 35.9 kms$^{-1}$has a 60 percent linear polarization, and its polarization direction is alignedwith the bipolar axis. Such a high degree of polarization suggests that maserinversion is due to radiative pumping. Five of the other maser features havesignificant linear polarization.