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Session 76 - Exploding Stars.
Display session, Thursday, June 13
Great Hall,
Five dwarf novae -- U Gem, VW Hyi, WX Hyi, YZ Cnc, and SS Cyg -- were observed in quiescence with the Hopkins Ultraviolet Telescope on Astro-2 in 1995 March. The far ultraviolet (830-1860 Åspectra of two of these dwarf novae --U Gem and VW Hyi -- show the broad Lyman line features and narrow metal absorption lines which are expected if the white dwarf dominates the UV emission. In U Gem, the strengths of the metal lines are close to those expected from a normal abundance WD atmosphere; in VW Hyi, the line strengths imply either that the abundances are substantially sub-solar or that there is a second source of emission which is diluting the WD spectrum. The spectra of the remaining systems show none of the features expected from a WD. Instead, the spectra of these dwarf novae -- WX Hyi, YZ Cnc, and SS Cyg -- are characterized by relatively blue continua extending shortward to the Lyman limit and broad emission lines. This suggests that these systems are dominated by emission from the disk or an extended disk atmosphere in the FUV. In this paper, we will describe the HUT observations of quiescent dwarf novae and our initial attempts to dissect the constituent components of their spectra.
Support for this work was provided by NASA contract NAS5-27000 to the Johns Hopkins University and NASA Grant NAG8-1074 to the Smithsonian Astrophysical Observatory.
