  Time-resolved spectra throughout the orbit of EF Eri during its low accretion
state were obtained with the Solar Blind Channel on the Advanced Camera for
Surveys onboard the Hubble Space Telescope. The overall spectral distribution
exhibits peaks at 1500 and 1700A, while the UV light curves display a
quasi-sinusoidal modulation over the binary orbit. Models of white dwarfs with
a hot spot and cyclotron emission were attempted to fit the spectral variations
throughout the orbit. A non-magnetic white dwarf with a temperature of ~10,000K
and a hot spot with central temperature of 15,000K generally matches the broad
absorptions at 1400 and 1600A with those expected for the quasimolecular H
features H2 and H+2 . However, the flux in the core of the Lyalpha absorption
does not go to zero, implying an additional component, and the flux variations
throughout the orbit are not well matched at long wavelengths. Alternatively, a
9500K white dwarf with a 100 MG cyclotron component can fit the lowest (phase
0.0) fluxes, but the highest fluxes (phase 0.5) require an additional source of
magnetic field or temperature. The 100 MG field required for the UV fit is much
higher than that which fits the optical/IR wavelengths, which would support
previous suggestions of a complex field structure in polars.
