Period échelle diagrams of l = 1 g modes for the example case described in Sect. 4.6. Left: frequencies of m = 0 (circles) and m = 1 (triangles) modes computed for a field with a radial extension σ_B = 0.003 R_★. Magnetic effects are treated either with a non-perturbative approach (red symbols), or a perturbative approach (gray symbols). Right: frequencies of m = 0 modes for values of σ = 0.0015 (red), 0.002 (green), and 0.003 (blue) and for a constant field (black).