AAS Meeting #193 - Austin, Texas, January 1999
Session 69. Circumstellar Material
Display, Friday, January 8, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[69.03] A Stellar movie: VLBA monitoring of SiO masers around the Mira variable TX Cam

P.J. Diamond, A.J. Kemball (NRAO)

Single dish monitoring of SiO masers around stars have revealed strong, cyclic variations of the spectra. The peak flux of the SiO masers appears to occur at a phase of 0.2 after the optical maximum, from phase 0.3 to 0.8 the average velocity of the spectrum appears to be slightly redshifted with respect to the mean velocity indicating infall of material. Recently Boboltz et al (1997) showed, using VLBA observations, that for the star R Aquarii the SiO masers were infalling at 4.3 km/s from optical phase 0.78 to 1.04. To date this has been the basis of our understanding of the nature of SiO variability.

We have been performing regular VLBA observations of the SiO masers around the Mira variable TX Cam. We have been taking data every two weeks and will eventually obtain 50 epochs covering 1.25 cycles of the star's phase. We shall present a movie of the structural changes occurring for the first 80% of our program, covering phases 0.3 to 1.3. We see complex structural changes including both infalling and outflowing gas. We also have information on the changing polarization structure of the masers. We shall discuss our observations in the context of the hydrodynamic models of Bowen.

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