active frequencies in the power spectrum and to optimize the S/N ratio, a Fourier analysis has been performed using the DFT algorithm of Deeming (1975) on the total UV continuum (sum of the five bands) and line (sum of NV, SiIV, CIV and HeII) fluxes and zero-order light. From Fig.2, the dominance of the $\Omega$ variability is apparent, being about twice the $\omega$ signal, as well as the presence of substantial power at the sideband and orbital harmonic frequencies. To distinguish real signals from artifacts due to the sampling of the HST orbit, a least-square technique was applied to the each data set which fits simultaneously multiple sinusoids at fixed frequencies. A synthetic light curve with the same temporal sampling of the data was created and subtracted (residuals). The continuum and zero-order light reveal, besides the $\omega$ and $\Omega$ frequencies, also the $\omega-2\,\Omega$, $\omega-\Omega$ and $\Omega+\omega$ sidebands, whereas in the emission lines the $2\,\Omega$ and $\omega-\Omega$ frequencies are detected. In Fig.2 the amplitude spectra relative to the multiple sinusoids and the residuals are also shown for comparison. It should be noted that peaks at $\rm \sim 54\,day^{-1}$ and $\rm \sim  84\,day^{-1}$ are identified as sideband fequencies of the spin and 