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VLBI Monitoring Observations of Water Masers Around the Semi-Regular Variable Star R Crateris

Jose K. Ishitsuka·Hiroshi Imai·Toshihiro Omodaka·Munetaka Ueno·Osamu Kameya·Tetsuo Sasao·Masaki Morimoto·Takeshi Miyaji·Jun-ichi Nakajima·Teruhiko Watanabe
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Abstract

We monitored water-vapor masers around the semi-regular variable star R Crateris with the Japanese VLBI Network (J-Net) at the 22 GHz band during four epochs with intervals of one month. The relative proper motions and Doppler-velocity drifts of twelve maser features were measured. Most of them existed for longer than 80 days. The 3-D kinematics of the features indicates a bipolar expanding flow. The major axis of the asymmetric flow was estimated to be at P.A. = 136 degrees. The existence of a bipolar outflow suggests that a Mira variable star had already formed a bipolar outflow. The water masers are in a region of apparent minimum radii of 1.3 x 10^12 m and maximum radii of 2.6 x 10^12 m, between which the expansion velocity ranges from 4.3 to 7.4 km/s. These values suggest that the water masers are radially accelerated, but still gravitationally bound, in the water-maser region. The most positive and negative velocity-drifting features were found relatively close to the systemic velocity of the star. We found that the blue-shifted features are apparently accelerated and the red-shifted apparently decelerated. The acceleration of only the blue-shifted features seems to be consistent with that of the expanding flow from the star.

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Jose K. Ishitsuka, Hiroshi Imai, Toshihiro Omodaka, Munetaka Ueno, Osamu Kameya, Tetsuo Sasao, Masaki Morimoto, Takeshi Miyaji, Jun-ichi Nakajima, Teruhiko Watanabe. 2001-12-13. VLBI Monitoring Observations of Water Masers Around the Semi-Regular Variable Star R Crateris. https://doi.org/10.1093/pasj%2F53.6.1231

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