SIMBAD references

We simulate the observations of proper motion of stars very close to the Galactic center. We show that the speckle interferometry done with the Keck II telescope is accurate enough to obtain orbital parameters for stars with the period P∼10 yr during ∼10 seasons of astrometric observations made once a year. The determination of a single orbit will give a central mass estimate with the typical uncertainty of the existing mass determinations based on velocity dispersion measurements. Much higher precision orbits will be measured in several years when the Keck Interferometer becomes operational and fainter stars are discovered even closer to Sgr A*. Astrometry alone will provide an accurate determination of M/D³, where M is the black hole mass and D is the distance to the Galactic center. If spectroscopic orbits of the stars are also measured, then both M and D will be precisely determined.