A long-term VLBA monitoring campaign of the v = 1, J = 1→0 SiO masers towards TX Cam - I. Morphology and shock waves

We present the latest and final version of themovie of the SiO masers towards the Mira variableTX Cam. The new version consists of 112 frames (78 successfully reduced epochs) with datacovering almost three complete stellar cycles between 1997 May 24 and 2002 January 25,observed with the Very Long Baseline Array. In this paper, we examine the global morphology, kinematics and variability of the masering zone. The morphology of the emission is confinedin a structure that usually resembles a ring or an ellipse, with occasional deviations due tolocalized phenomena. The ring appears to be contracting and expanding, although for the firstcycle contraction is not observed. The width and outer boundary of the masering zone followthe stellar pulsation. Our data seem to be consistent with a shock being created once per stellarcycle at maximum that propagates with a velocity of ~7 km s^-1. The difference in velocitiesalong different axes strongly suggests that the outflow in TX Cam is bipolar. The contributionof projection is examined and our results are compared with the latest theoretical model.