Testing the third-body hypothesis in the cataclysmic variables LU Camelopardalis, QZ Serpentis, V1007 Herculis and BK Lyncis

Abstract

ABSTRACT Some cataclysmic variables (CVs) exhibit a very long photometric period (VLPP). We calculate the properties of a hypothetical third body, initially assumed to be on a circular–planar orbit, by matching the modelled VLPP to the observed one of four CVs studied here: LU Camelopardalis, QZ Serpentis, V1007 Herculis and BK Lyncis. The eccentric and low inclination orbits for a third body are considered using analytical results. The chosen parameters of the binary components are based on the orbital period of each CV. We also calculate the smallest corresponding semimajor axis permitted before the third body’s orbit becomes unstable. A first-order analytical post-Newtonian correction is applied, and the rate of precession of the pericentre is found, but it cannot explain any of the observed VLPP. For the first time, we also estimate the effect of secular perturbations by this hypothetical third body on the mass transfer rate of such CVs. We made sure that the observed and calculated amplitude of variability was also comparable. The mass of the third body satisfying all constraints ranges from 0.63 to 97 Jupiter masses. Our results show further evidence supporting the hypothesis of a third body in three of these CVs, but only marginally in V1007 Herculis.