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Time-resolved spectra throughout the orbit of EF Eri during its low accretionstate were obtained with the Solar Blind Channel on the Advanced Camera forSurveys onboard the Hubble Space Telescope. The overall spectral distributionexhibits peaks at 1500 and 1700A, while the UV light curves display aquasi-sinusoidal modulation over the binary orbit. Models of white dwarfs witha hot spot and cyclotron emission were attempted to fit the spectral variationsthroughout the orbit. A non-magnetic white dwarf with a temperature of ~10,000Kand a hot spot with central temperature of 15,000K generally matches the broadabsorptions at 1400 and 1600A with those expected for the quasimolecular Hfeatures H2 and H+2 . However, the flux in the core of the Lyalpha absorptiondoes not go to zero, implying an additional component, and the flux variationsthroughout the orbit are not well matched at long wavelengths. Alternatively, a9500K white dwarf with a 100 MG cyclotron component can fit the lowest (phase0.0) fluxes, but the highest fluxes (phase 0.5) require an additional source ofmagnetic field or temperature. The 100 MG field required for the UV fit is muchhigher than that which fits the optical/IR wavelengths, which would supportprevious suggestions of a complex field structure in polars.

Analyzing the Low State of EF Eridani with Hubble Space Telescope Ultraviolet Spectra