Research on Galactic dynamics with maser sources

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The purpose of this research was to investigate the rotation curve of the Galaxt by measuring the radial velocities of maser sources with high accuracy that is now available with techniques in radio astronomy. The high sensitivity radio observations extends the method of positional astronomy, which were based on the observations on nearby stars, to all the way in the Galaxy. We have measured radial velocities of SiO and OH/H2O masers ources, obtained the rotation curve of the Galaxy, and clarify the difference of motion between the gas and stars. We also tested a possibility of measuring proper motions of nearby maser sources. we have identified the maser sources with infrared JHK imaging observations : positions of stars were measured in an accuracy of arcsec, and determined the distances from the spectral energy distribution in the near and mid infrared data.With the analyzes of the data obtained by these radio and near-infrared observations, we have obtained the foolowing results ;(1) The radial velocity data of SiO maser sources at the outer Galaxy show that the Galactic rotation curve is slowly decreasing with radius near the solar neibourhood, and the oxygen-and carbon-rich stars have a different characteristic in the near-infrared color index.(2) We founda number of SiO maser sources in the directions of Sgr B molecular cloud and they are identified at the near-infrared imaging as stars. We also found many SiO maser sources within 1 arc minute from the Galactic center.(3) Analyzes the positional and velocity data of water maser spots revealed the presence of accelerating motion of the maser spots.Based on these observations, we have confirmed the possibility of measuring stellar motions in the Galaxy with high accuracy by the method combining the radio and infrared techniques.