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Paper: The evolution of disks and winds in dwarf novae outbursts
Volume: 261, The Physics of Cataclysmic Variables and Related Objects
Page: 337
Authors: Froning, C. S.; Long, K. S.; Drew, J. E.; Knigge, C.; Proga, D.; Mattei, J. A.
Abstract: Far ultraviolet (FUV) observations are excellent probes of the inner accretion disk, disk outflows, and the mass-accumulating white dwarf in cataclysmic variables. Here we study the contrasting behavior of two canonical dwarf novae in outburst by presenting FUSE FUV (904 - 1187Å) spectroscopy of U Gem and SS Cyg. We observed each system four times during a single outburst. The outburst peak and early decline spectra of SS Cyg are well fit by models of a steady-state accretion disk and a biconical wind. A broad, blueshifted O VI wind-formed absorption line is the only strong spectral feature. In late outburst decline, O VI and C III lines are seen as broad emission features and the continuum has flattened. In U Gem, the continua of the optical outburst plateau spectra are plausibly fit by accretion disk model spectra. The spectra also show numerous narrow, low-velocity absorption lines that do not originate in the inner accretion disk. We discuss the line spectra in the context of partial absorption of the FUV continuum by low-velocity, vertically-extended material located at large disk radii. The late outburst decline spectrum of U Gem is dominated by the white dwarf. WD model fits confirm the sub-solar C and super-solar N abundances found in earlier studies.
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