Osamu Kameya

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 . .. . .. . .. . ..

SiO maser survey of AGB stars in the North Galactic Cap

A SiO maser survey in the J =1 0, v = 1 and 2 transitions has been made for IRAS sources in the North Galactic Cap (b > 30) with the Nobeyama 45 m radio telescope. The sources were selected on the basis of their IRAS 12/25-m and 25/60-m flux ratios as likely oxygen-rich AGB candidates. SiO masers were detected from 24 out of the 97 selected sources, where 17 were new detections. The distances and heights above the Galactic plane are calculated. The Galactic distribution of detected and undetected stars indicates that metallicity is likely to govern the detection rate. The Galactocentric angular velocities of the subsampled stars are derived and their variation with the Galactic height is discussed.

Phase Solution Analysis for the Simultaneous Dual Frequency VLBI Observation

Taehyun Jung, Bong Won Sohn, Hideyuki Kobayashi, Tetsuo Sasao, Tomoya Hirota, Osamu Kameya, Yoon Kyung Choi, Hyun Soo Chung a Korea Astronomy and Space Science Institute, Daejeon, Republic of Korea University of Science and Technology, Daejeon, Republic of Korea Mizusawa VERA Observatory, NAOJ, Mitaka, Tokyo, Japan Ajou University, Suwon 442-749, Republic of Korea Max-Planck-Institut fur Radioastronomie, Bonn, Germany E-mail: thjung@kasi.re.kr

Galactic rotation measurements based on H 2 O maser astrometry with VERA

We present results of astrometric observations of S269 H2O maser performed with VERA (VLBI Exploration of Radio Astrometry). We have monitored the positions of S269 H2O masers for 1 year and successfully detected its parallax to be 189± 8 micro-arcsecond. This corresponds to a source distance of 5.28 .24 −0 .22 kpc, and is the smallest parallax (and thus the largest distance) that has ever been measured by means of annual parallax. Proper motions of S269 H2O maser were also measured and used to determine the Galactic rotation velocity at the position of S269. Our measurements show that the Galactic rotation velocity at S269 is the same to that at the Sun within 3%, indicating that the Galactic rotation curve is flat out to R∼13 kpc.