Eclipse timing modelling of three post-common envelope binaries: hybrid solutions

Abstract

ABSTRACT We report 90 new observations of three post-common envelope binaries at primary eclipse spanning between 2018 December and 2022 February. We combine recent primary eclipse timing observations with previously published values to search for substellar circumbinary components consistent with timing variations from a linear ephemeris. We used a least-squares minimization fitting algorithm weighted by a Hill orbit stability function, followed by Bayesian inference, to determine best-fitting orbital parameters and associated uncertainties. For HS2231+2441, we find that the timing data are consistent with a constant period and that there is no evidence to suggest orbiting components. For HS0705 + 6700, we find both one- and two-component solutions stable for at least 10 Myr. For HW Vir, we find three- and four-component solutions that fit the timing data reasonably well, but are unstable on short time-scales, and therefore highly improbable. Conversely, solutions calculated using a Bayesian orbit stability prior result in a poor fit. The stable solutions significantly deviate from the ensemble timing data in both systems. We speculate that the observed timing variations for these systems, and very possibly other sdB binaries, may result from a combination of substellar component perturbations and an Applegate–Lanza mechanism.