The Position of Sagittarius A*. II. Accurate Positions and Proper Motions of Stellar SiO Masers near the Galactic Center

Menten, Reid, Eckart and Genzel (1997) accurately determined the position ofSgr A* on an infrared image, by aligning the infrared image with positionsmeasured for SiO masers, associated with infrared-bright evolved stars, atradio wavelengths. We now report greatly improved radio positions and, for thefirst time, proper motions of many stellar SiO masers at the Galactic Center.These positions and motions, coupled with better infrared imaging, allow a muchimproved location of Sgr A* on infrared images. With current data, infraredstars can be placed in a reference frame tied to Sgr A*, to an accuracy ofapproximately 10 mas in position and 1 mas/yr in motion. The position of Sgr A*is, within uncertainties, consistent with stellar accelerations and themeasured orbital focus of the star S2. The star S2 was observed within 16 mas(130 AU in projection) of Sgr A* on 2002 May 02. Finally, we find that thecentral stellar cluster moves with Sgr A* to within approximatly 70 km/s.Comment: 27 pages, 6 figures, and 6 table