Eclipse Timing Modeling of Three Post-Common Envelope Binaries: Hybrid Solutions

TL;DR

This study analyzes eclipse timing variations in three post-common envelope binaries, finding some potential circumbinary companions but also highlighting the instability and complexity of such models, suggesting alternative explanations for timing variations.

Contribution

The paper introduces a hybrid modeling approach combining least-squares fitting and Bayesian inference to assess circumbinary companions in post-common envelope binaries.

Findings

HS2231+2441 shows no evidence of orbiting companions.

Stable multi-component solutions are possible for HS0705+6700.

Unstable solutions fit HW Vir's data but are unlikely due to short-term instability.

Abstract

We report 90 new observations of three post common envelope binaries at primary eclipse spanning between December 2018 to February 2022. 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-fit 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 timescales, 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.