Upper panel: period vs. period ratio values for all GYRE time steps. The gray band is the initial period range, the red cross marks the allowed FM period and period ratio in the double-mode phase. Lower panel: same as above, but only showing the segments for the initial drop in period at the beginning of the TP, with the arrow indicating the direction of change. The black line highlights the 1.7 M_⊙ model, the first that clearly traverses the cross.