The extraordinary cataclysmic binary RU Pegasi: The hottest white dwarf in a dwarf nova?

We present the results of the first multicomponent synthetic spectral analysis of International Ultraviolet Explorer (IUE) archival spectra of the long-period dwarf nova RU Peg during quiescence. The best-fit, high-gravity, solar composition photosphere models yield T-eff = 50,000-53,000 K with scale factor distances of 250 pc. Optically thick accretion disk models imply accretion rates between 1 x 10(-9) and 1 x 10(-10) M-. yr(-1) in order to match the steeply sloping far-UV continuum. However, the best-fit accretion disk models yield distances from 600 to 1300 pc, well beyond the estimated distance range of 130 300 pc. Using rough theoretical flux arguments and the distance estimates, we find better agreement between the observed far-UV luminosity and the predicted far-UV luminosity of a hot, massive, white dwarf model than with an accretion disk model. RU Peg appears to contain the hottest white dwarf yet found in a dwarf nova. We cannot rule out that the far-UV energy distribution is due to a multitemperature white dwarf with cooler, more slowly rotating higher latitudes and a rapidly spinning, hotter equatorial belt. We discuss implications of our analysis for theoretical predictions of the disk instability theory of dwarf nova outbursts. We discuss a comparison between RU Peg's white dwarf and the observed properties of other analyzed white dwarfs in dwarf novae.