Stability of co-orbitals as a function of log ₁₀(μ) and Δa/a. The initial conditions are ζ₀ = π/ 3 and Δa/a ∈ [ 0,0.06 ]: vertical purple line in Fig. 2. The black line indicates the separatrix between the tadpole and the horseshoe domains. The dots follow a curve Δa ∝ μ^{1 / 3}, delimiting the stability region of the horseshoe domain. The colour code indicates the value of the libration frequency, i.e. log ₁₀(ν/n) (see Fig. 4 for the scale).