Upper panel: the ratio P_mag/P_EUV vs. the orbital semimajor axis a for the known transiting planets computed for a stellar radial magnetic field (s = 2). The value of P_mag given by Eq. (4) has been multiplied by 1/6 (see the text). The dotted horizontal line corresponds to P_mag = P_EUV. Middle panel: the same as the upper panel, but for s = 2.5 corresponding to a non-linear force-free stellar field. Lower panel: the same as the upper panel, but for s = 3, corresponding to a potential dipole stellar field.