Evolutionary sequence of 1.2 M_⊙ stellar models in the HR diagram, from the zero-age main sequence to the tip of the RGB. The solid line represents the domain where a coupling between the core and the envelope is possible and mixed modes can be observed, unlike the dashed line. The red stars represent the three models (SG, YR and ER) considered as examples in Fig. 1. The square qualitatively labels the transition point from a Type-a evanescent region to a Type-b evanescent region.