We present the ultraviolet spectrum of the SW Sex star and nova-like variable DW UMa in an optical low state , as observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope ( HST ) .
The data are well described by a synthetic white dwarf ( WD ) spectrum with T _ { eff } = 46 , 000 \pm 1000 K , \log { g } = 7.60 \pm 0.15 , v \sin { i } = 370 \pm 100 km s ^ { -1 } and Z / Z _ { \odot } = 0.47 \pm 0.15 .
For this combination of T _ { eff } and \log { g } , WD models predict M _ { WD } = 0.48 \pm 0.06 M _ { \odot } and R _ { WD } = ( 1.27 \pm 0.18 ) \times 10 ^ { 9 } cm .
Combining the radius estimate with the normalization of the spectral fit , we obtain a distance estimate of d = 830 \pm 150 pc .

During our observations , DW UMa was approximately 3 magnitudes fainter in V than in the high state .
A comparison of our low-state HST spectrum to a high-state spectrum obtained with the International Ultraviolet Explorer shows that the former is much bluer and has a higher continuum level shortward of 1450 Å .
Since DW UMa is an eclipsing system , this suggests that an optically thick accretion disk rim blocks our view of the WD primary in the high state .
If self-occulting accretion disks are common among the SW Sex stars , we can account for ( i ) the preference for high-inclination systems within the class and ( ii ) their V-shaped continuum eclipses .
Moreover , even though the emission lines produced by a self-obscured disk are generally still double-peaked , they are weaker and narrower than those produced by an unobscured disk .
This may allow a secondary line emission mechanism to dominate and produce the single-peaked , optical lines that are a distinguishing characteristic of the SW Sex stars .