Two-dimensional schematic representing the two deformed bodies. The star is divided into three masses: the central one of mass M_⋆ − 2μ_⋆ at S, and two bulges of mass μ_⋆ at S′ and S′′. Planet j is divided into three masses: the central one of mass M_pj − 2μ_pj at P_j, and two bulges of mass μ_pj at and . Ω_⋆ is the star rotation vector (its norm is Ω_⋆, the star rotation frequency), Ω_pj is planet j rotation vector (its norm is Ω_pj, the planet rotation frequency), and is a vector collinear with the orbital angular momentum of planet j (its norm is equal to the derivative of the true anomaly). e_rj is the radial vector.