LS Pegasi: A low-inclination SW Sextantis-type cataclysmic binary with high-velocity Balmer emission-line wings

We present time-resolved spectroscopy and photometry of the bright cataclys mic variable LS Peg (=S193; V approximate to 13.0-Szkody et al.). The Balme r lines exhibit broad, asymmetric wings Doppler-shifted bi about 2000 km s( -1) at the edges, while the He I Lines show phase-dependent absorption feat ures strikingly similar to SW Sextantis stars, as well as emission through most of the phase. The C III/N III emission blend does not show any phase d ependence. From velocities of H alpha emission Lines, we determine an orbit al period of 0.174774 +/- 0.000003 days (=4.1946 hr), which agrees with Szk ody's value of approximately 4.2 hr. No stable photometric signal was found at the orbital period. A noncoherent quasi-periodic photometric signal was seen at a period of 20.7 +/- 0.3 minutes. The high-velocity Balmer wings most probably arise from a stream reimpact p oint close to the white dwarf. We present simulated spectra based on a kine matic model similar to the modified disk-overflow scenario of Hellier & Rob inson. The models reproduce the broad line wings, though some other details are unexplained. Using an estimate of dynamical phase based on the model, we show that the phasing of the emission- and absorption-line variations is consistent with that in (eclipsing) SW Sex stars. We therefore identify LS Peg as a low-inclination SW Sex star. Our model suggests i = 30 degrees, and the observed absence of any photomet ric signal at the orbital frequency establishes i < 60 degrees. This constr aint puts a severe strain on interpretations of the SW Sex phenomenon which rely on disk structures lying slightly out of the orbital plane.