LS Pegasi: A Low‐Inclination SW Sextantis–Type Cataclysmic Binary with High‐Velocity Balmer Emission‐Line Wings 11Based in part on observations obtained at MDM Observatory, operated by Dartmouth College, Columbia University, the Ohio State University, and the University of Michigan.

Abstract

ABSTRACTWe present time‐resolved spectroscopy and photometry of the bright cataclysmic variable LS Peg (=S193; V ≈ 13.0—Szkody et al.). The Balmer lines exhibit broad, asymmetric wings Doppler‐shifted by about 2000 km s−1 at the edges, while the He i lines show phase‐dependent absorption features strikingly similar to SW Sextantis stars, as well as emission through most of the phase. The Ciii/N iii emission blend does not show any phase dependence. From velocities of Hα emission lines, we determine an orbital period of 0.174774 ± 0.000003 days (=4.1946 hr), which agrees with Szkody'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 point close to the white dwarf. We present simulated spectra based on a kinematic model similar to the modified disk‐overflow scenario of Hellier & Robinson. 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°, and the observed absence of any photometric signal at the orbital frequency establishes i<60°. This constraint puts a severe strain on interpretations of the SW Sex phenomenon which rely on disk structures lying slightly out of the orbital plane.