Observations of SiO Maser Sources within a Few Parsecs from the Galactic Center

Shuji Deguchi (1), Takahiro Fujii (2), Makoto Miyoshi (3), Jun-ichi Nakashima (4)


(1) Nobeyama Radio Observatory, National Astronomical Observatory,, Minamimaki, Minamisaku, Nagano 384-1305
(2) Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181-8588
(3) VERA Office, National Astronomical Observatory, Mitaka, Tokyo 181-8588
(4) Department of Astronomical Science, The Graduate University for Advanced Studies,, Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1305

Paper: PASJ, Feb 2002, in press


Abstract:

Mapping and monitoring observations of the SiO maser sources near the Galactic center were made with the Nobeyama 45-m telescope at 43 GHz. Rectangular mapping an area of approximately 200'' * 100'' in a 30'' grid, and triangular mapping in a 20'' grid toward the Galactic center, resulted in 15 detections of SiO sources; positions of the sources were obtained with errors of 5-10'' except for a few weak sources. Three-year monitoring observations found that the component at V_lsr=-27 km s-1 of IRS 10 EE flared to about 1.5 Jy during 2000 March-May, which was a factor of more than 5 brighter than its normal intensity. Using the radial velocities and positions of the SiO sources, we identified 5 which are counterparts of the previously observed OH 1612 MHz sources. The other 10 SiO sources have no OH counterparts, but two were previously detected with VLA, and four are located close to the positions of large-amplitude variables observed at near-infrared wavelengths. A least-square fit to a plot of velocities versus Galactic longitudes gives a rather high speed for rotation of the star cluster around the Galactic center. The observed radial-velocity dispersion is roughly consistent with the value obtained before. It was found that all the SiO sources with OH 1612 MHz counterparts have periods of light variation longer than 450 days, while SiO sources without OH masers often have periods shorter than 450 days. This fact suggests that lower-mass AGB stars are more often detected in SiO masers than in the OH 1612 MHz line.


Preprints available from the authors at deguchi@nro.nao.ac.jp , or the raw TeX (no figures) if you click here.

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