Structure of Sagittarius A* at 86 GHz using VLBI closure quantities

At radio wavelengths, images of the compact radio source Sagittarius A* (Sg r A*) in the Galactic center are scatter broadened with a lambda (2) depend ence due to an intervening ionized medium. We present VLBI observations of Sgr A* at 86 GHz using a six station array, including the VLBA antennas at Pie Town, Fort Davis, and Los Alamos, the 12 m antenna at Kitt Peak, and th e millimeter arrays at Hat Creek and Owens Valley. To avoid systematic erro rs due to imperfect antenna calibration, the data were modeled using interf erometric closure information. The data are best modeled by a circular Gaus sian brightness distribution of FWHM 0.18 +/- 0.02 mas. The data are also s hown to be consistent with an elliptical model corresponding to the scatter ing of a point source. The source structure in the north-south direction, w hich is less well determined than in the east-west direction because of the limited north-south u-v coverage of the array, is constrained to be less t han 0.27 mas by these measurements. These results are consistent with extra polations of intrinsic structure estimates obtained with VLBI at a 7 mm wav elength, assuming the intrinsic size of Sgr A* has a greater dependence tha n lambda (0.9) with wavelength.