  Non-axisymmetric oscillations of rapidly rotating relativistic stars are
studied using the Cowling approximation. The oscillation spectra have been
estimated by Fourier transforming the evolution equations describing the
perturbations. This is the first study of its kind and provides information on
the effect of fast rotation on the oscillation spectra while it offers the
possibility in studying the complete problem by including spacetime
perturbations. Our study includes both axisymmetric and non-axisymmetric
perturbations and provides limits for the onset of the secular bar mode
rotational instability. We also present approximate formulae for the dependence
of the oscillation spectrum from rotation. The results suggest that it is
possible to extract the relativistic star's parameters from the observed
gravitational wave spectrum.
