Mouchet, K. Mukai, S.R. Rosen'
date: 'Received June 15, 1999 ; accepted September 2, 1999 '
title: 'Time-resolved HST and IUE UV spectroscopy of the Intermediate Polar FO Aqr[^1]'
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Introduction
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Intermediate Polars (IPs) are a subclass of magnetic Cataclysmic Variables which consist of an asynchronously rotating ($\rm P_{spin} < P_{orb}$) magnetized white dwarf accreting from a late type, main sequence, Roche-lobe filling secondary star (Patterson 1994; Warner 1995).

Except for a few systems for which polarized optical/IR emission is detected, the white dwarf is believed to possess a weak ($\la$ 2MG) magnetic field which dominates the accretion flow only at a few radii from its surface. Within the magnetospheric radius, material is channeled towards the magnetic polar regions in an arc-shaped accretion curtain (Rosen et al. 1988). At larger distances, different accretion patterns can be present: a truncated accretion disc (disc-fed systems), direct accretion from the stream onto the magnetosphere (disc-less systems) as well as a combination of the two, where the stream material overpasses the disc (disc-overflow) (Hellier 1995 and references therein).

Due to the asynchronous rotation, IPs show a wide range of periodicities at the white dwarf spin ($\omega$), the orbital ($\Omega$) and sideband frequencies (Warner 