  It has been recently argued through numerical work that rotating stars with a
high degree of differential rotation are dynamically unstable against bar-mode
deformation, even for values of the ratio of rotational kinetic energy to
gravitational potential energy as low as O(0.01). This may have implications
for gravitational wave astronomy in high-frequency sources such as core
collapse supernovae. In this paper we present high-resolution simulations,
performed with an adaptive mesh refinement hydrodynamics code, of such low
T/|W| bar-mode instability. The complex morphological features involved in the
nonlinear dynamics of the instability are revealed in our simulations, which
show that the excitation of Kelvin-Helmholtz-like fluid modes outside the
corotation radius of the star leads to the saturation of the bar-mode
deformation. While the overall trends reported in an earlier investigation are
confirmed by our work, we also find that numerical resolution plays an
important role during the long-term, nonlinear behaviour of the instability,
which has implications on the dynamics of rotating stars and on the attainable
amplitudes of the associated gravitational wave signals.
