Kinematics of the Tucana Dwarf Galaxy: An Unusually Dense Dwarf in the
  Local Group
  We present new FLAMES$+$GIRAFFE spectroscopy of 36 member stars in the
isolated Local Group dwarf spheroidal galaxy Tucana. We measure a systemic
velocity for the system of $v_{\mathrm{Tuc}}=216.7_{-2.8}^{+2.9}$kms$^{-1}$,
and a velocity dispersion of
$\sigma_{\mathrm{v,Tuc}}=14.4_{-2.3}^{+2.8}$kms$^{-1}$. We also detect a
rotation gradient of $\frac{dv_{r}}{d\chi}=7.6^{+4.2}_{-4.3}$ kms$^{-1}$
kpc$^{-1}$, which reduces the systemic velocity to
$v_{\mathrm{Tuc}}=215.2_{-2.7}^{+2.8}$ kms$^{-1}$ and the velocity dispersion
to $\sigma_{v,\mathrm{Tuc}}=13.3_{-2.3}^{+2.7}$ kms$^{-1}$. We perform Jeans
modelling of the density profile of Tucana using the line--of--sight velocities
of the member stars. We find that it favours a high central density consistent
with `pristine' subhalos in $\Lambda$CDM, and a massive dark matter halo
($\sim$$10^{10}$\,M$_\odot$) consistent with expectations from abundance
matching. Tucana appears to be significantly more centrally dense than other
isolated Local Group dwarfs, making it an ideal laboratory for testing dark
matter models.
