Far Ultraviolet Spectroscopic Explorer Observations of the Dwarf Nova SW Ursae Majoris during Quiescence

• Published in: The Astrophysical journal Vol. 617; no. 1; pp. 500 - 507
• Main Authors: Povich, M. S, Raymond, J. C, Lobel, A, Menou, K
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 10.12.2004; University of Chicago Press
• Subjects: Astronomy; Binary and multiple stars; Cataclysmic binaries (novae, dwarf novae, recurrent novae, and nova-like objects). Symbiotic stars; Earth, ocean, space; Exact sciences and technology; Novae, dwarf novae, recurrent novae, and other cataclysmic (eruptive) variables; Stars; Variable and peculiar stars (including novae); Light curves; Ultraviolet spectra; Satellite observation; Dwarf novae; Accretion disks; Resonance line; FUSE satellite; Quiescence; Close binary stars; Cataclysmic variable stars; Hydrogen molecules; Oxygen ions; Emission line; Short period variable star; Spectroscopical observation
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/425213

We present spectroscopic observations of the short-period cataclysmic variable SW UMa obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite while the system was in quiescence. The data include the resonance lines of O VI at 1031.91 and 1037.61 AA. These lines are present in emission, and they exhibit both narrow ( similar to 150 km s super(-1)) and broad ( similar to 2000 km s super(-1)) components. The narrow O VI emission lines exhibit unusual double-peaked and redshifted profiles. We attribute the source of this emission to a cooling flow onto the surface of the white dwarf primary. The broad O VI emission most likely originates in a thin, photoionized surface layer on the accretion disk. We searched for emission from H sub(2) at 1050 and 1100 AA, motivated by the expectation that the bulk of the quiescent accretion disk is in the form of cool, molecular gas. If H sub(2) is present, then our limits on the fluxes of the H sub(2) lines are consistent with the presence of a surface layer of atomic H that shields the interior of the disk. These results may indicate that accretion operates primarily in the surface layers of the disk in SW UMa. We also investigate the far-UV continuum of SW UMa and place an upper limit of 15,000 K on the effective temperature of the white dwarf.