  Due to the large masses, heavy-flavor quarks are dominantly produced in
initial hard scattering processes and experience the whole evolution of the
medium produced in heavy-ion collisions at RHIC energies. They are also
expected to thermalize slower than light-flavor quarks. Thus the measurement of
heavy quark production and azimuthal anisotropy can provide important insights
into the medium properties through their interactions with the medium.
  In these proceedings, we report measurements of $D^0$ production and elliptic
flow ($v_2$) via topological reconstruction using STAR's recently installed
Heavy Flavor Tracker (HFT). The new measurement of the nuclear modification
factor ($R_{AA}$) of $D^0$ mesons in central Au+Au collisions at
$\sqrt{s_{NN}}$ = 200 GeV confirms the strong suppression at high transverse
momenta ($p_{T}$) reported in the previous publication with much improved
precision. We also report the measurement of elliptic flow for $D^0$ mesons in
a wide transverse momentum range in 0-80% minimum-bias Au+Au collisions. The
$D^0$ elliptic flow is finite for $p_{T}$ $>$ 2 GeV/c and is systematically
below that of light hadrons in the same centrality interval. Furthermore,
several theoretical calculations are compared to both $R_{AA}$ and $v_2$
measurements, and the charm quark diffusion coefficient is inferred to be
between 2 and $\sim$12.
