arXiv · 0808.1151
VLBI Astrometry of AGB Variables with VERA -- A Semiregular Variable S Crateris --
Abstract
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.
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Akiharu Nakagawa, Miyuki Tsushima, Kazuma Ando, Takeshi Bushimata, Yoon Kyung Choi, Tomoya Hirota, Mareki Honma, Hiroshi Imai, Kenzaburo Iwadate, Takaaki Jike, Seiji Kameno, Osamu Kameya, Ryuichi Kamohara, Yukitoshi Kan-Ya, Noriyuki Kawaguchi, Masachika Kijima, Mi Kyoung Kim, Hideyuki Kobayashi, Seisuke Kuji, Tomoharu Kurayama, Toshihisa Maeda, Seiji Manabe, Kenta Maruyama, Makoto Matsui, Naoko Matsumoto, Takeshi Miyaji, Takumi Nagayama, Kayoko Nakamura, Daisuke Nyu, Chung Sik Oh, Toshihiro Omodaka, Tomoaki Oyama, Nicolas Pradel, Satoshi Sakai, Tetsuo Sasao, Katsuhisa Sato, Mayumi Sato, Katsunori M. Shibata, Hiroshi Suda, Yoshiaki Tamura, Kousuke Ueda, Yuji Ueno, Kazuyoshi Yamashita. 2008-08-08. VLBI Astrometry of AGB Variables with VERA -- A Semiregular Variable S Crateris --. https://doi.org/10.1093/pasj%2F60.5.1013
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