Coherence and stochastic resonance in a birhythmic van der Pol system René Yamapi, André Chéagé Chamgoué, Giovanni Filatrella and Paul Woafo Eur. Phys. J. B, 90 8 (2017) 153 Published online: 09 August 2017 DOI: 10.1140/epjb/e2017-80118-4