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 Hei lines, but both the He ii λ4686 and the metallic lines (e.g. Cii λ4267 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−l 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.