Orbital Period of the Low‐Inclination SW Sextantis Star V442 Ophiuchi

Abstract

V442 Ophiuchi is a low-inclination (noneclipsing) nova-like cataclysmic variable. We have obtained medium resolution (1-3.5 A), time-resolved optical spectroscopy of this interacting binary star spanning an interval of 4 yr, from 1995 August to 1999 June. Using an Hα radial velocity curve constructed from our combined spectroscopic data sets, we have determined that Porb = 0.1243 days for V442 Oph, breaking the long-standing 1 day alias ambiguity in its orbital period. V442 Oph shares many of the characteristics of the group of cataclysmic variables known as the SW Sextantis stars. Its Doppler tomograms and orbital phase-dependent emission-line behavior, including the occurrence of a prominent transient absorption event, are consistent with those of other SW Sex stars. V442 Oph also displays single-peaked rather than double-peaked emission lines, strong He II λ4686 emission, and a phase offset of +0.08 between the Hα emission-line radial velocities and the phasing of He II. We discuss the role of V442 Oph as one of three known low-inclination examples of SW Sex stars. Like the other low-inclination SW Sex stars, LS Pegasi and V795 Herculis, the Balmer emission lines in V442 Oph have high velocity components that extend to ≈±1900 km s-1 and follow an apparent S-wave pattern in the trailed spectrum. Finally, we compare two models for the SW Sex stars involving accretion stream overflow, in the context of a low-inclination system in which our line of sight likely extends over the entire face of the disk.