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 ^ { \circ } .
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 \times 10 ^ { 12 } m and maximum radii of 2.6 \times 10 ^ { 12 } m , between which the expansion velocity ranges from 4.3 to 7.4 km s ^ { -1 } .
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 .