Abstract
We have measured the polarization properties of the J = 2..-->..1, v = 1 SiO circumstellar maser emission from R Cas over a period of nearly 2 years. Velocity profiles for both the Stokes parameter I and the total linear polarization change relatively smoothly but not periodically with time indicating that radiative pumping mechanisms are probably not dominant in this source. Superposed on these smoothly varying profiles, we have detected a phase dependent effect at phiapprox.0.96 for two successive optical maxima. This phase dependent effect, most readily observed in polarized radiation, places the SiO just above the stellar photosphere and allows the radial thickness of the line formation region to be estimated. We report the detection of a ''superbroad'' spectral feature of width approx.18 km s/sup -1/.
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