2024ApJ...961...97Z

We present an effective strategy for extensive analysis of eclipsing time variations (ETVs) using modern and sophisticated optimization methods that comprise a set of tools to investigate period variability mechanisms in eclipsing binary stars such as the light-time effect, the Applegate mechanism, and mass transfer. We implement these methods for the first time assuming that the above mechanisms can act simultaneously in the puzzling W UMa-type binary star TZ Bootis by using archival and new TESS data spanning 75 yr and reexamining the up-to-date ETVs. Preliminary analysis of the TESS data revealed for the first time the presence of a second binary in agreement with previous spectroscopic data and astrometric results from Gaia DR3. We consider the most credible scenario for the ETV: two stellar circumbinary companions of minimum masses M₃ = 0.5 M_☉ and M₄ = 0.14 M_☉ in highly eccentric orbits e₃ = 0.70 and e₄ = 0.82 with periods P₃ = 38 yr and P₄ = 20 yr along with a 24 yr magnetic activity of the secondary component and a long-term period increase (dP/dt = 1.2 × 10^–8 days yr^–1), interpreted as a conservative mass transfer from the secondary to the primary component at a rate of dM₁/dt = 3.7 × 10^–9 days yr^–1. Further spectroscopic observations, analytical modeling of the second pair, and ETV analysis of both pairs are needed to investigate the quadruple nature of the system.