Detection of a Possible Bipolar Outflow Around the Semi-Regular Variable Star R Crateris by the Japanese VLBI Network (J-Net)

Abstract

We have monitored water vapor masers around the semi-regular variable star R Crateris (R Crt) with the Japanese VLBI Network (J-Net) at the 22 GHz band at four epochs with intervals of one month. With a typical positional accuracy of 0.5 mas in the R.A. and 0.6 mas in the declination directions, and with a velocity resolution of 0.105 km s-1, we were able to measure twelve relative proper motions and radial-velocity drifts of maser features. 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°. The existence of a bipolar outflow suggests that an evolved star had already formed a bipolar outflow at the early phase of the AGB star