Period scan for ellipsoidal shape. The colorbar marks the model RMS. For clarity, points with RMS values above 0.25 are not plotted. The best-fit value with the lowest RMS is marked with a red point and corresponds to the values in Table 2. The pink square marks the second best solution. The two dashed vertical lines mark the two best periods found by the period analysis described in Section 3. The thick horizontal and vertical lines show the separations ΔP_ψ and ΔP_ϕ between local minima (see the main text).