Observational Study of the SiO Maser Sources at the Galactic Center Region

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This research explores the physics in the environment near the galactic center with measuring the radial velocities of stars in the silicon monoxide (SiO) maser lines from late type stars by a radio telescope. We have completed the following radio and infrared observations in Hl0 and H11 academic years. (1) 600 color-selected IRAS sources in the galactic disk have been observed in SiO maser lines with the 45-m radio telescope at Nobeyama., resulting 300 detection. From analyzing the obtained radial velocities of stars, we found a group of the stars being deviant from the galactic rotation which was known from the gas motion. (2) We made the JHK photometric and imaging observations for about 500 sources in the same region with the Australian National Univ. 2.3-m infrared telescope. From the apparent magnitudes, we estimated the distances to the objects.From this research, the following facts are revealed. (1) large percentages of IRAS sources which are located within 10 degree from the galactic center are considered to be the bulge stars. A subset of stars located in front of the galactic center exhibits a large negative (-46 km/s) average radial velocity, and those behind, a positive radial velocity,. Here the distance were deduced from the infrared intensities at 12 and 25 micron. (3) This phenomenon is interpreted as a streaming motion of stars in the bar-like bulge; the near end of the bar is located at the first quadrant of the galactic longitude and the stellar orbits are elongated along the bar potential. Dr. S. Deguchi planned and directed the research and analyzed the near-infrared photometric data. Dr. Miyoshi analyzed the radio spectral data and performed the VLBI observations.