2025RAA....25h5002B

We present a comprehensive analysis of BI CVn, an eclipsing overcontact binary system. New BVR photometric observations, combined with available spectroscopic data, were analyzed simultaneously using the Wilson-Devinney method to derive the orbital and physical parameters of the system. The resulting stellar parameters are M₁ = 0.58 ± 0.01M_⊙, M₂ = 1.42 ± 0.02M_⊙, R₁ = 0.88 ± 0.01R_⊙, R₂ = 1.31 ± 0.01R_⊙, with an orbital separation of a = 2.80 ± 0.01R_⊙. Based on all available CCD times of minimum light, including both ground-based and TESS observations, the (O - C) diagram of BI CVn was analyzed. The orbital period exhibits a long-term decrease at a rate of -2.3239 (±0.0001) × 10^–8 day yr^–1, likely due to mass transfer from the more massive to the less massive component. Superimposed on this trend is a cyclic variation with a period of 56.84 ± 0.08 yr, indicative of a light-travel time effect caused by a third body, whose estimated mass is 0.63 ± 0.02M_⊙. Using these derived parameters, we modeled the binary's evolution through non-conservative processes with the Binary Star Evolution code. The evolutionary tracks of the components were examined in multiple parameter planes, leading to an estimated merger timescale of approximately 2.70 Gyr.