  High frequency quasi-periodic oscillations (HF QPOs) are observed in the
X-ray power-density spectra (PDS) of several microquasars and low mass X-ray
binaries. Many proposed QPO models are based on oscillations of accretion
toroidal fluid structures orbiting in the vicinity of a compact object. We
study oscillating accretion tori orbiting in the vicinity of a Kerr black hole.
We demonstrate that significant variation of the observed flux can be caused by
the combination of radial and vertical oscillation modes of a slender,
polytropic, perfect fluid, non-self-graviting torus with constant specific
angular momentum. We investigate two combinations of the oscillating modes
corresponding to the direct resonance QPO model and the modified relativistic
precession QPO model.
