NSVS 14256825: period variation and orbital stability analysis of two possible substellar companions

Abstract

Recent period investigations of the Post-Common Envelop Binary (PCEB) NSVS 14256825 suggested that two circumbinary companions were necessary to explain the observed Eclipse Timing Variations (ETVs). Our objective was to search for the best-fitting curve of two LTTE terms in the ETV diagram, implementing a grid search optimization scheme of Keplerian (kinematic) and Newtonian (N-body) fits, alongside a dynamical stability analysis of N-body simulations. We compiled two datasets of archival photometric data covering a different timeline and updated them with new observations and with three new times of minima (TOMs) calculated from the Transiting Exoplanet Survey Satellite (\textit{TESS}). A grid search optimization process was implemented and the resulted solutions, that fell within the $90\%$ confidence interval of the best-fitting curve of the ETV diagram, were tested for orbital stability using N-body simulations and the MEGNO chaos indicator. The Keplerian and Netwonian fits are in close agreement and hundreds of stable configurations were identified for both datasets reaching a lifetime of 1 Myr. Our results suggest that the ETV data can be explained by the presence of a circumbinary planet with mass $m_b=11 M_{Jup.}$ in a nearly circular inner orbit of period $P_b = 7$ yr. The outer orbit is unconstrained with a period range $P_c=20-50$ yr (from 3:1 to 7:1 MMR) for a circumbinary body of substellar mass ($m_c=11-70 M_{Jup.}$). The stable solutions of the minimum and maximum reduced chi-square value were integrated for 100 Myr and confirmed a non-chaotic behavior. Their residuals in the ETV data could be explained by a spin-orbit-coupling model (Applegate-Lanza). Continuous monitoring of the system is required in order to refine and constrain the proposed solutions.