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J. A. Urban, E. M. Sion (Villanova University)
We have extracted many of the IUE archival SWP spectra of dwarf novae in quiescence and uniformly analyzed them using synthetic spectral codes for accretion disks, stellar photospheres, absorbing curtains and accretion belts. The study included nearly all systems successfully observed (i.e., adequate S/N) by IUE, both above and below the period gap. All of the spectra were de-reddened when needed and corrected for systematic errors in the final IUE flux calibration by applying the algorithm of Massa & Fitzpatrick (2000). Distances were adopted from ground-based, Hubble FGS and Hipparcos parallaxes, or from correlations between absolute visual magnitude at the peak of outburst versus orbital period, derived from the parallax work of Johnson et al. (2003), or from Warner (1995). The sample consisted of 52 systems of all dwarf nova subtypes, 17 of which were also observed with HST. Overall, 46% of the systems are disk-dominated (i.e. an accretion disk accounts for > 60% of the FUV flux), while 42% of the systems are white dwarf-dominated (i.e., the white dwarf accounts for > 60% of the FUV flux). In 12% of the systems, the white dwarf and accretion disk each provide between 40% and 60% of the FUV flux. White dwarf-dominated systems comprise 35% of the dwarf novae below the gap and only 7% of the systems above the gap. We present newly determined accretion rates in quiescence, white dwarf temperatures and discuss the implications of our study for disk accretion physics and CV evolution.
This research was supported by NASA grant NAG5-11182 and by NSF grant AST99-01955 to Villanova University. Support was also provided in part by summer undergraduate research support from the Delaware Space Grant Consortium.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.