the $\Omega$ frequency, while a variability at the spin is at a 2$\sigma$ level. No significant variations are detected in the equivalent width of the absorption as well as in the emission component.

In contrast to the flux behaviour, the V/R ratios are variable only at the $\omega$ frequency (Fig.2, bottom panels). Noteworthy is the marginal spin variability in the CIV line. The amplitudes of the spin modulation, obtained from the least-square fits, are reported in the last column of Table2.

Optical data
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The analysis of BVRI data acquired during three nights has been performed following the same procedure adopted for the HST data. Contrary to previous observations, the orbital variability also dominates in the optical being $\sim$ 1.5 times the spin modulation. The presence of sideband modulations is more uncertain because of the lower quality of the data. Nevertheless, to ensure uniformity between UV and optical results, a least-square fit to the data has been applied using the same five frequency sinusoidal function, i.e. $\Omega$, $\omega$, $\omega-2\,\Omega$, $\omega-\Omega$, $\omega+\Omega$. The resulting amplitudes, reported in Table 2, when compared with the noise in the residuals (column 8), can be considered as upper limits.

As far as the fast photometry 