Observations of the SW Sextantis Star DW Ursae Majoris with theFar Ultraviolet Spectroscopic Explorer

We present an analysis of the first far-ultraviolet observations of the SWSextantis-type cataclysmic variable DW Ursae Majoris, obtained in November 2001with the Far Ultraviolet Spectroscopic Explorer. The time-averaged spectrum ofDW UMa shows a rich assortment of emission lines (plus some contamination frominterstellar absorption lines including molecular hydrogen). Accretion diskmodel spectra do not provide an adequate fit to the far-ultraviolet spectrum ofDW UMa. We constructed a light curve by summing far-ultraviolet spectraextracted in 60-sec bins; this shows a modulation on the orbital period, with amaximum near photometric phase 0.93 and a minimum half an orbit later. No otherperiodic variability was found in the light curve data. We also extractedspectra in bins spanning 0.1 in orbital phase; these show substantial variationin the profile shapes and velocity shifts of the emission lines during anorbital cycle of DW UMa. Finally, we discuss possible physical models that canqualitatively account for the observed far-ultraviolet behavior of DW UMa, inthe context of recent observational evidence for the presence of aself-occulting disk in DW UMa and the possibility that the SW Sex stars may bethe intermediate polars with the highest mass transfer rates and/or weakestmagnetic fields.Comment: accepted by the Astronomical Journal; 36 pages, including 12 figures and 4 table