Values for the wind termination shock obtained from simulation A (black) at the end of each evolutionary phase, compared to R_B for the three magnetic field strengths. At 5 μG  (red), the magnetic field can never stop the expansion of the circumstellar bubble perpendicular to the field and the 10 μG  (green) field will do so, but only at the very end of the main sequence. The 20 μG  (blue) field will stop expansion throughout most of the stellar evolution.