We have produced a movie of the time evolution of the v = 1, J = 1--0 43 GHz SiO masers in the inner circumstellar envelope of the isolated Mira variable TX Cam. Our observations, taken every two weeks with the VLBA, currently cover about 60% of the stellar cycle from φ ~ 0.6 --> φ ~1.2. They show that, in contrast to previous observations and theoretical models, the gas in which the masers are embedded is undergoing expansion during this period with a typical velocity of 3.65 +/- 0.15 km/s. Some isolated features are seen to start falling back towards the star at around φ ~1.0. We suggest that the 5 --> 10 G magnetic fields we have previously detected at the position of the SiO masers may explain the departure from the expected behaviour.
|Original language||English (US)|
|Title of host publication||Asymptotic Giant Branch Stars|
|Editors||T. Le Bertre, A. Lebre, C. Waelkens|
|State||Published - 1999|