Abstract
All three orbits for doubly eclipsing system (2+2) BU CMi were significantly refined using new TESS data and published spectral observations. New values of apsidal motion and accurate physical parameters of the system are obtained. Component A: \({{T}_{1}} = 9860 \pm 50\) K, \({{M}_{1}} = (2.7 \pm 0.15){\kern 1pt} {{M}_{ \odot }}\) , \({{R}_{1}} = (2.19 \pm 0.07){\kern 1pt} {{R}_{ \odot }}\) , \({{T}_{2}} = 10\,000 \pm 80\) K, \({{M}_{2}} = (2.7 \pm 0.15){\kern 1pt} {{M}_{ \odot }}\) , \({{R}_{2}} = (2.23 \pm 0.07){\kern 1pt} {{R}_{ \odot }}\) , apsidal period \({{P}_{{{\text{aps}}}}} = 25.06\) years. Component B: \({{T}_{1}} = 10\,260 \pm 80\) K, \({{M}_{1}} = (2.7 \pm 0.15){\kern 1pt} {{M}_{ \odot }}\) , \({{R}_{1}} = (2.33 \pm 0.02){\kern 1pt} {{R}_{ \odot }}\) , \({{T}_{2}} = 9700 \pm 50\) K, \({{M}_{2}} = (2.5 \pm 0.15){\kern 1pt} {{M}_{ \odot }}\) , \({{R}_{2}} = (2.04 \pm 0.02){\kern 1pt} {{R}_{ \odot }}\) , \({{P}_{{{\text{aps}}}}} = 25.22\) years. Orbiting period \({{P}_{{{\text{orb}}}}} = (5.88 \pm 0.03)\) years. Photometric parallax exactly equals Gaia DR3 value \(\pi =0.00401'' \) . The age of the system is determined to be 224 Myr at solar chemical composition. The work is partially based on a talk presented at the Modern Stellar Astronomy 2025 Conference.
