VLBI OBSERVATIONS OF THE GALACTIC-CENTER SOURCE SGR A-ASTERISK AT 86 GHZ AND 215 GHZ

We have observed and detected Sgr A with VLBI at 86 GHz and at 215 GH z in March 1995. At &6 GHz the measured closure phase is close to zero , consistent with a point-like or symmetric structure of 190 +/- 30 mu as in size. At 215 GHz we have detected SgrA with a signal-to-noise ratio of 6. This yields a tentative size estimate of 110 +/- 60 mu as which, despite of a limited calibration accuracy and uncertainty in th e origin of the nm/sub-mm total Aux density excess, lies well above th e scattering size of 20 mu as at this frequency. The intrinsic size of Sgr A thus appears to be 17 +/- 9 Schwarzschild radii for a 2.6.10(6 ) M-. black hole.