Left: distribution of T_eff at the surface in one hemisphere of the primary, projected in the plane XZ for several combinations of the mass ratio q = M₂/M₁ and the filling factor ρ. Right: logarithmic plot of T_eff versus g_eff for the same cases. Solid lines are linear fits to the data and the corresponding value of the gravity darkening exponent β is indicated in the plots. For comparison, von Zeipel’s law (β = 0.25) is shown by a dashed line. In the second row an inset shows the small dispersion of the points around the fitting power law. The last case (q = 0) corresponds to an isolated star rotating with angular velocity Ω = 0.854Ω_k. Normalised values of effective temperature and gravity are defined in Eq. (22).