VY CMa is a supergiant star surrounded by a red reflection nebulae. It is a highly luminous infrared source and displays OH, H2O and SiO masers. The Silicon Monoxide masers around VY CMa are particularly strong. These masers are situated only a few stellar radii from the stellar surface, giving us insight into the properties of the extended atmosphere. The polarization of these masers may yield information about the magnetic field of the star.
I am studying 43 GHz SiO masers around VY CMa, using the Very Long Baseline Array. Very long baseline interferometry, VLBI, provides a means to resolve the individual maser components, giving milliarcsecond scale images of the maser region.
I will discuss masers in general, the properties of VY CMa, and the technique of spectral line polarization VLBI. My initial maps will be presented, along with an interesting polarization feature.