The far-ultraviolet spectrum and short-timescale variability of AM Herculis from observations with the Hopkins Ultraviolet Telescope

Using the Hopkins Ultraviolet Telescope (HUT), we have obtained 850-1850 An gstrom spectra of the magnetic cataclysmic variable star AM Her in the high state. These observations provide high time resolution spectra of AM Her i n the far-ultraviolet and sample much of the orbital period of the system. The spectra are not well modeled in terms of simple white dwarf (WD) atmosp heres, especially at wavelengths shortward of Ly alpha. The continuum flux changes by a factor of 2 near the Lyman limit as a function of orbital phas e; the peak fluxes are observed near magnetic phase 0.6 when the accreting pole of the WD is most clearly visible. The spectrum of the hot spot can be modeled in terms of a 100,000 K WD atmosphere covering 2% of the WD surfac e. The high time resolution of the HUT data allows an analysis of the short -term variability and shows the UV luminosity to change by as much as 50% o n timescales as short as 10 s. This rapid variability is shown to be incons istent with the clumpy accretion model proposed to account for the soft X-r ay excess in polars. We see an increase in narrow-line emission during thes e flares when the heated face of the secondary is in view. The He II narrow -line flux is partially eclipsed at secondary conjunction, implying that th e inclination of the system is greater than 45 degrees. We also present res ults from models of the heated face of the secondary. These models show tha t reprocessing on the face of the secondary star of X-ray/EUV emission from the accretion region near the WD can account for the intensities and kinem atics of most of the narrow-line components observed.