Left panel: evolution of the radius of the bubble as a function of the time for various 25 M_⊙ models. All models are normalised for the time of log (t  [yr] ) = 4.5. The extension of the bubble at this time is about 0.75 pc, with small deviations for the different models. Right panel: same for the 60 M_⊙ models. Here the extension of the bubble for the normalisation time is about 1.7 pc. Thin lines indicate slopes of 3/5, 2/5, and 1/5.