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Published online by Cambridge University Press: 12 April 2016
In this Note we study perturbed isotropic harmonic oscillators in 1–1–1 resonance, which is one of the typical cases of galactic potential models. We focus on cubic and quartic axial symmetric potentials giving explicitly their normal form. The 3D normalized Hénon and Heiles case, which requires to reach fourth order, is studied showing its relative equilibria and bifurcations.