Starspot Activity and Third-body Perturbations in the Eclipsing Binary KIC 9451096

Abstract

We investigate the short-period Algol-type (EA-type) eclipsing binary system KIC 9451096 using high-precision space-based photometry from Kepler and the Transiting Exoplanet Survey Satellite (TESS) , complemented by ground-based observations from the Sierra Remote Observatories (SRO), which provide additional constraints on system properties. Eclipse timing variations (ETVs) are analyzed using more than 2000 eclipse timings, consisting of approximately 1000 primary and 1000 secondary minima. The timing data are examined using the light-travel time effect (LTTE) model and discrete Fourier transform (DFT) techniques to search for periodic modulations in the O–C diagram. The combined eclipse-timing and frequency analyses reveal three characteristic timescales: the 1.25 day orbital period, a dominant ∼85 day modulation consistent with LTTE induced by a tertiary companion, and secondary ∼5.2 day variability that is most plausibly associated with magnetic activity. The LTTE solution yields a minimum tertiary mass of M3 ≈ 0.0487 M⊙ (∼51MJup), assuming a total mass of 1.83 M⊙ for the eclipsing pair. This is consistent with a brown dwarf in a nearly circular orbit. Light-curve modeling with PHOEBE 2.4.21 demonstrates that evolving starspots on the secondary component can reproduce the observed O’Connell effect. This supports the interpretation that magnetic activity contributes to the observed ∼5.2 day modulation. The LTTE and eclipse-timing analyses support the scenario in which KIC 9451096 is a hierarchical triple system containing a brown-dwarf tertiary companion, while the starspot modeling provides a complementary physical interpretation of the observed short-timescale photometric and timing variability associated with magnetic activity.