  The evolution of a nonaxisymmetric bar-mode perturbation of rapidly rotating
stars due to a secular instability induced by gravitational wave emission is
studied in post-Newtonian simulations taking into account gravitational
radiation reaction. A polytropic equation of state with the polytropic index
$n=1$ is adopted. The ratio of the rotational kinetic energy to the
gravitational potential energy $T/|W|$ is chosen in the range between 0.2 and
0.26. Numerical simulations were performed until the perturbation grows to the
nonlinear regime, and illustrate that the outcome after the secular instability
sets in is an ellipsoidal star of a moderately large ellipticity $\agt 0.7$. A
rapidly rotating protoneutron star may form such an ellipsoid, which is a
candidate for strong emitter of gravitational waves for ground-based laser
interferometric detectors. A possibility that effects of magnetic fields
neglected in this work may modify the growth of the secular instability is also
mentioned.
