Astrometry of AGB Variables with VERA: Annual Parallax and the Orbit of SY Sculptoris in the Galaxy

作者：Nyu Daisuke^*; Nakagawa Akiharu; Matsui Makoto; Imai Hiroshi; Sofue Yoshiaki; Omodaka Toshihiro; Kurayama Tomoharu; Kamohara Ryuichi; Hirota Tomoya; Honma Mareki; Shibata Katsunori M; Kobayashi Hideyuki; Iwadate Kenzaburo; Miyaji Takeshi

来源：Publications of the Astronomical Society of Japan, 2011, 63(1): 63-70.

• astrometry
• masers(H2O)
• stars: AGB and post-AGB
• stars: individual(SY Sculptoris)

We report on the results of astrometric observations of H2O masers toward a Mira variable, SY Sculptoris (SY Scl), with the VLBI Exploration of Radio Astrometry (VERA) from 2006 October to 2008 October. We determined that SY Scl's annual parallax is 0.75 +/- 0.03 mas, corresponding to a distance of 1.33 +/- 0.05 kpc. SY Scl is 1.3 kpc south of the Galactic plane and moves approximately south from the plane with a velocity of 63 +/- 2 km s(-1) with respect to the LSR. From the present position and motion, we calculated SY Scl's orbit for the last 1 Gyr based on a parametrized model of the Galactic gravitational potential. SY Scl has an orbit as a member of the Galactic thick disk stars. Subtracting the averaged absolute proper motions of masers, we derived an internal motion of H2O masers in SY Scl. The kinematics of the masers is consistent with motion in a single plane. The masers around SY Scl were found to be distributed in an area of 70 AU x 80 AU, corresponding to 15 times as large as the stellar photosphere diameter of 5 AU. Based on the measured distance and apparent magnitude of SY Scl, we find the absolute magnitude of SY Scl to be M-K = -8.07 +/- 0.08 mag. This is approximately consistent with the value of -8.09 +/- 0.07 mag, which was derived from the Galactic Mira period luminosity relation (2008, MNRAS, 386, 313).

• 出版日期2011
• 单位中国科学院国家天文台