The 43-GHz SiO maser in the circumstellar envelope of the asymptotic giant branch star R Cassiopeiae

We present multi-epoch, total intensity, high-resolution images of 43-GHz, nu = 1, J = 1-0 SiO maser emission towards the Mira variable R Cassiopeiae (R Cas). In total, we have 23 epochs of data for R Cas at approximate monthly intervals over an optical pulsation phase range from phi = 0.158 to 1.78. These maps show a ring-like distribution of the maser features in a shell, which is assumed to be centred on the star at a radius of 1.6-2.3 times the radius of star, R-star. It is clear from these images that the maser emission is significantly extended around the star. At some epochs, a faint outer arc can be seen at 2.2R(star). The intensity of the emission waxes and wanes during the stellar phase. Some maser features are seen infalling as well as outflowing. We have made initial comparisons of our data with models by Gray et al.