  We present proper motions for $>$40 stars at projected distances $\leq1.2''$
from Sagittarius A* (Sgr A*). We find evidence on a $\geq2\sigma$ level for
radial anisotropy of the cluster of stars within $1''$ of Sgr A*. We find no
evidence for a stationary source or variable source at the position of Sgr A*.
We confirm/find accelerated motion for 6 stars, with 4 stars having passed the
pericenter of their orbits during the observed time span. We
calculated/constrained the orbital parameters of these stars. All orbits have
moderate to high eccentricities. We discuss the possible bias in detecting
preferentially orbits with high eccentricities. We find that the center of
acceleration for all the orbits coincides with the radio position of Sgr A*.
  From the orbit of the star S2, the currently most tightly constrained one, we
determine the mass of Sgr A* to be $3.3\pm0.7\times10^{6}$M$_{\odot}$ and its
position to $2.0\pm2.4$ mas East and $2.7\pm4.5$ mas South of the nominal radio
position. The mass estimate for the central dark mass from the orbit of S2 is
fully consistent with the mass estimate of $3.4\pm0.5\times10^{6}$M$_{\odot}$
obtained from stellar proper motions within $1.2''$ of Sgr A* using a
Leonard-Merritt mass estimator. We find that radio astronomical observations of
the proper motion of Sgr A* in combination with its intrinsic source size place
at the moment the tightest constraints on the mass density of Sgr A*, which
must exceed $\rho_{\mathrm{Sgr
A*}}>3\times10^{19}\mathrm{M}_{\odot}\mathrm{pc}^{-3}$.
