VLBI Astrometry of AGB Variables with VERA -- A Semiregular Variable S Crateris

We present a distance measurement for the semiregular variable S Crateris (S Crt) based on its annual parallax. With the unique dual beam system of the VLBI Exploration for Radio Astrometry (VERA) telescopes, we measured the absolute proper motion of a water maser spot associated with S Crt, referred to the quasar J1147-0724 located at an angular separation of 1.23\(^{\circ}\). In observations spanning nearly two years, we have detected the maser spot at the LSR velocity of 34.7 km s\(^{-1}\), for which we measured the annual parallax of 2.33\(\pm\)0.13 mas corresponding to a distance of 430\(^{+25}_{-23}\) pc. This measurement has an accuracy one order of magnitude better than the parallax measurements of HIPPARCOS. The angular distribution and three-dimensional velocity field of maser spots indicate a bipolar outflow with the flow axis along northeast-southwest direction. Using the distance and photospheric temperature, we estimate the stellar radius of S Crt and compare it with those of Mira variables.