A Movie of a Star: Multiepoch Very Long Baseline Array Imaging of the SiO Masers toward the Mira Variable TX Cam
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Abstract
We describe an observing campaign using the Very Long Baseline Array (VLBA) to monitor the time-evolution of the v=1, J=1-0 SiO maser emission towards the Mira variable TX Cam. The data reported here cover the period 1997 May 24 to 1999 February 19, during which the SiO maser emission was imaged at approximately bi-weekly intervals. The result is an animated movie at an angular resolution of ~500 microarcsec, over a full pulsation period, of the gas motions in the near circumstellar environment of this star, as traced by the SiO maser emission. This paper serves to release the movie and is the first in a series concerning the scientific results from this observing campaign. In this paper, we discuss the global proper motion of the SiO maser emission as a function of pulsation phase. We measure a dominant expansion mode between optical phases $\phi \sim 0.7-1.5$ confirming ballistic deceleration, and compare this to predictions from existing pulsation models for late-type, evolved stars. Local infall and outflow motions are superimposed on the dominant expansion mode, and non-radial local gas motions are also evident for individual SiO maser components. The overall morphology and evolution of the SiO emission deviates significantly from spherical symmetry, with important implications for models of pulsation kinematics in the near-circumstellar environments of Mira variables.
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