V795 Her: An SW Sex star in the period gap?

Abstract

We present optical photometry and spectroscopy of the nova-like variable V795 Her. The emission lines exhibit an extremely complex structure consisting of several time-variable emission and absorption components. We confirm the spectroscopic modulation of 0.1082 d which we attribute to the orbital period of the system. The equivalent widths (EWs) of all the emission lines are strongly modulated on this period, showing a pronounced minimum around phase 0.5. We associate this minimum with the transit of an absorption feature which drives dramatic line changes, seen as transient double peaks and P Cygni type profiles. The absorption depth grows with the excitation level in Balmer and He I lines, but both the He II λ 4686 and the metallic lines (e.g. C II λ 4267 and the Bowen blend) are entirely in emission. The centroid of the Hα emission (which is contaminated very little by the absorption feature) is delayed by 83° with respect to the high-excitation lines. We assume that the latter trace the orbital motion of the primary, enabling us to define an absolute zero-phase. High-velocity S-waves are clearly observed in all Balmer lines, with amplitudes of about 1750 km s-1 and maximum redshift at about phase 0. However, our high-resolution spectra suggest that these can be separated into two phased components, with γ-velocities of ∼ ±750 km s-1 and K ∼ 1000 km s-1, Probably formed in accretion columns on the white dwarf. In addition, the H I cores exhibit the presence of low-velocity (K = 268 km s-1) S-waves, roughly phased with their high-amplitude partners. On the other hand, our R-band photometry is dominated by flickering with no evidence for modulation with the orbital period nor the previously reported 0.1165-d periodicity. Based on the spectral properties, we propose that V795 Her is a new SW Sex star, observed at intermediate inclination. The complex behaviour of V795 Her can be qualitatively explained invoking an intermediate polar scenario with a synchronously rotating white dwarf.