PoS(10th EVN Symposium)073 The 43 GHz SiO Maser in the Circumstellar Envelope of AGB star R Cassiopeia K. A. Assaf JBCA, The Allan Turing Building, School of Physics & Astronomy, The University of Manchester, Oxford Road, Manchester, M13 0EW, UK E-mail: kam@ jb.man.ac.uk P. J. Diamond Chief, Astronomy & Space Science CSIRO, PO Box 76, Epping NSW 1710 E-mail: Philip.Diamond@csiro.au A. M. S. Richards JBCA, The Allan Turing Building, School of Physics & Astronomy, The University of Manchester, Oxford Road, Manchester, M13 0EW, UK E-mail: amsr@jb.man.ac.uk Abstract We present multi-epoch total intensity images of 43 GHz, v=1, J=1-0 SiO maser emission toward the Mira variable R Cas. These data were taken as part of a more extensive programme of observations of other stars. In total we have 23 epochs of data for R Cas. Data were recorded at each VLBA antenna in dual-circular polarization in two 4 MHz windows, each digitally sampled at the full Nyquist rate of 8 Mbps in 1-bit quantization at approximate monthly sampling over an optical pulsation phase range of ϕ = 0.158 to ϕ = 1.78. These maps show a ring-like distribution of the maser features in the shell which is assumed to be centered on the star at a distance of 1.9→2.3 times the radius of star (R * ) from the star's centre. It is clear from this image that the maser emission is significantly extended around the star. At some epochs a faint outer arc can be seen at 2.2 R * . The intensity of the emission waxes and wanes during the stellar phase. Some maser features are seen infalling as well as out flowing. We are attempting to reconstruct the 3-D velocity field and comparing the result with models of Gray et. al. 2009. 10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation of radio arrays Manchester, UK September 20-24, 2010  Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it