EXTREME-ULTRAVIOLET SPECTROSCOPY AND PHOTOMETRY OF VV-PUPPIS DURING A HIGH ACCRETION STATE

We determine the physical properties of the accretion region of the AM Her-type binary VV Puppis using extreme ultraviolet (EUV) medium-resolution spectroscopy and photometry obtained with the Extreme Ultraviolet Explorer (EUVE) observatory. The EUV continuum from VV Pup was detected in the wavelength range from 75 to 135 Angstrom and was simultaneously recorded with the Deep Survey/Spectrometer (DS/S) imaging telescope, allowing for the extraction of an accurate light curve. VV Pup appeared to have entered a high-accretion state just prior to the pointed EUVE observations. We use the EW light curve to infer the diameter of the accretion region (d = 220 km) assuming a hemispherical geometry and a radius of 9000 km for the white dwarf. We perform a model atmosphere analysis and, based on the light curve properties and assuming a distance of 145 pc, we derive an effective temperature of the accretion region in the range 270,000 < T-eff < 360,000 K and a neutral hydrogen column density in the local interstellar medium of n(H) = 1.9-3.7 x 10(19) cm(-2). The total EUV/soft X-ray energy radiated by the accretion region is similar to 3.5 x 10(32) ergs s(-1). Our results provide a first verification of past suggestions that deep heating of the white dwarf surface produces the soft X-ray flux from the polars. We present a possible detection of O VI absorption features, and we suggest that extensive EUVE observations targeting high-accretion events may result in oxygen and heavier element abundance determinations in the accretion region.