VLBI and polarimetric observations of the SiO masers in R Cassiopeiae

The spatial structure, polarization characteristics, and temporal variability of the SiO emission in the v = 1, J = 1 approaching 0 masing transition from the late-type star R Cassiopeia were studied. From VLBI observations, it was found that the emission regions are clumpy. Some regions show well-defined polarization characteristics. The maser regions are distributed over a projected area having a diameter of several stellar radii. The variations in the flux density from all regions occur in phase with the star's optical variations. The coincidence of these variations puts a lower limit on the speed with which the pumping mechanism interacts with the masing regions. Polarization characteristics derived from the high spatial resolution VLBI experiment are similar to those obtained from the low spatial resolution (single antenna) measurements. 29 references.