Evolution of the Magnetic Fields of Main-Sequence CP-Stars. III

Estimates of the ages of magnetic stars show that the oldest have ages of t = 10⁹ years. The theoretical calculations are confirmed by indications that the damping constant for the magnetic field owing to ohmic losses is τ ≫10⁹ years. This also supports the assumption that, prior to the onset of convection, there are no reasons for decay of the magnetic field in the atmospheres of magnetic stars other than ohmic damping. The time variation of the surface magnetic field is actually determined only by two simultaneously acting, oppositely directed factors: a decrease in the field with increasing stellar radius and an increase owing to the relaxation of small structures. Additional data show that the reduction in the average surface magnetic field with the evolutionary increase in a star’s radius essentially has a cubic dependences. This confirms the assumption that the large-scale magnetic field approaches a dipole configuration.