Observational Study of the Massive Black Hole SgrA* and its Surrounding Field

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1) We performed VLBA observations of several SiO masers around the massive black hole, SgrA* at the Galactic center. We detected proper motions of the three out of them with accuracy about 0.1mas/year. The results suggest that SgrA* may move relative to the surrounding stars. We also found the lower limit of the mass within 2 pc from the Galactic center is 2*10^6 solar mass.2) Using the Nobeyama Millimeter wave Interferometer we monitored the flux density of SgrA* for short time flaring. There observed no flare of SgrA* within the observing session from Dec 2004 to May 2005.3) We derived the mass (including dark matter) within 30 pc from the Galactic center by analyzing the statistics of line of sight velocities of SiO maser emissions from late type stars and by the use of integration of the Bolzmann equation along the line of sight. Unlike the distribution of OH masers, the one of the SiO masers follows the square of the distance from the Galactic center. Assuming that the central mass is the sum of the mass of central black hole and stellar system with the square law, we can make an equation of momentum of velocities from the line of sight integration of Bolzmann equation.The mass of the Galactic center is M R=(2.69±1.30]+0.88[±0.07](R/pc)^{1.25)×10^6 solar mass.