A long-term VLBA monitoring campaign of the v=1, J=1-0 SiO masers toward TX Cam - I. Morphology and Shock Waves

TL;DR

This study uses VLBA data over three stellar cycles to analyze the morphology, kinematics, and shock wave phenomena in SiO masers around TX Cam, revealing bipolar outflows and pulsation-related zone dynamics.

Contribution

It provides a comprehensive long-term VLBA monitoring dataset and analysis of SiO maser morphology, shock waves, and bipolar outflows in TX Cam, enhancing understanding of stellar pulsation effects.

Findings

Masers form a ring or ellipse with variable morphology.

Shock waves propagate with ~7 km/s, recurring each stellar cycle.

Evidence of bipolar outflows in the masering zone.

Abstract

We present the latest and final version of the movie of the SiO masers toward the Mira variable TX Cam. The new version consists of 112 frames (78 successfully reduced epochs) with data covering almost three complete stellar cycles between 24 May 1997 to 25 January 2002, observed with the VLBA. In this paper we examine the global morphology, kinematics and variability of the masering zone. The morphology of the emission is confined in a structure that usually resembles a ring or an ellipse, with occasional deviations due to localised phenomena. The ring appears to be contracting and expanding, although for the first cycle contraction is not observed. The width and outer boundary of the masering zone follow the stellar pulsation. Our data seem to be consistent with a shock being created once per stellar cycle at maximum that propagates with a velocity of ~7 km/s. The difference in velocities along different axes strongly suggests that the outflow in TX Cam is bipolar. The contribution of projection is examined and our results are compared with the latest theoretical model.