a) Estimated sizes of the planetary magnetospheres along a planetary year assuming three different values of the polar planetary magnetic field: 10, 50, and 100 G. b) Predicted maximum frequency of the radio emission of V830 Tau b. This frequency is calculated at the border of the polar-cap boundary, which is located at different colatitudes depending on the size of the planet magnetosphere (cf., Eq. (A.1)). The magnetic field intensity at this position in shown in the right axis.