  Sagittarius A*, the supermassive compact object at the center of the Galaxy,
exhibits outbursts in the near infrared and X-ray domains. These flares are
likely due to energetic events very close to the central object, on a scale of
a few Schwarzschild radii. Optical interferometry will soon be able to provide
astrometry with an accuracy of this order (~10 muas). In this article we use
recent photometric near infrared data observed with the adaptive optics system
NACO at the Very Large Telescope combined with simulations in order to deploy a
method to test the nature of the flares and to predict the possible outcome of
observations with the Very Large Telescope Interferometer. To accomplish this
we implement a hot spot model and investigate its appearance for a remote
observer in terms of light curves and centroid tracks, based on general
relativistic ray tracing methods. First, we use a simplified model of a small
steady source in order to investigate the relativistic effects qualitatively. A
more realistic scenario is then being developed by fitting our model to
existing flare data. While indications for the spin of the black hole and
multiple images due to lensing effects are marginal in the light curves,
astrometric measurements offer the possibility to reveal these high-order
general relativistic effects. This study makes predictions on these astrometric
measurements and leads us to the conclusion that future infrared
interferometers will be able to detect proper motion of hot spots in the
vicinity of Sagittarius A*.
