  Time resolved spectroscopy of the Intermediate Polar FO Aqr reveals the
presence of multiple periodicities in the UV range. A strong orbital modulation
dominates both continuum and emission line flux variabilities, while line
velocity motions are only detected at the rotational frequency. A prominent
orbital periodicity is also observed in coordinated optical photometry, where
FO Aqr was previously found to be spin dominated. The spectral dependence of
the main periodicities shows the presence of multi-temperature components in FO
Aqr and for the first time a hot and a cool component in the rotational
modulation. From a comparison with previous UV and optical data obtained in
1990, no spectral variations in the orbital and rotational variabilities are
detected, indicating no significant changes in the effects of X-ray
illumination but rather a shrinking of the accretion curtain accompained by an
increase in size of the thickened part of the accretion disc. These
observations, consistent with the recently discovered long term trend in the
X-ray pulsation amplitudes, independently confirm a change in the accretion
mode in FO Aqr, which switched from a disc-fed into a disc-overflow state,
likely triggered by mass accretion variations.
