The Position and Proper Motion of Sgr A*

M. J. Reid1, K. M. Menten2, R. Genzel3, T. Ott3, R. Schödel3, & Eckart, A.4

1 Harvard-Smithsonian Center for Astrophysics
2 Max-Planck-Institut für Radioastronomie
3 Max-Planck-Institut für extraterrestrische Physik
4 University of Köln

E-mail contact: reid@cfa.harvard.edu

Sgr A* has been located on infrared images of the Galactic Center with a 2 sigma accuracy of 60 mas by Menten et al (1997), and the absolute proper motion of Sgr A* has been determined with an accuracy of about 20 km/s by Reid et al (1999) and Backer & Sramek (1999). These observations revealed that Sgr A* is very faint at 2 microns and appears to be at rest at the dynamical center of the Galaxy. Since these observations, significant advances in infrared imaging and radio astrometry have occurred. Both the location of Sgr A* and its absolute proper motion have been improved by a factor of about three. These advances improve the infrared limits on emission from Sgr A*, constrain stellar orbit determinations, and tighten the lower limit on the mass directly tied to the compact radio source Sgr A*.