MAGNETIC BRAKING IN SINGLE AND BINARY STARS

We discuss the basic concept and the problems of magnetic braking via magnetically controlled hot plasmas in late-type stars. We investigate the magnetic braking process in special magnetic field structures in both single stars and binaries. We find that in single solar-type star s, the high-order component of the observed complicated fields can acc ount for the braking rate of the present Sun. However, this component cannot account for the braking rate of young solar-type stars, even th ough this field is much stronger than the simple (monopolar or dipolar ) field usually adopted in braking models. For magnetically interactin g cataclysmic binaries, the magnetic fields of the white dwarf greatly change the magnetic fields on the main-sequence secondaries. In parti cular, in synchronously rotating magnetic CVs (AM Herculis systems) ma gnetic braking may even turn off if the white dwarf magnetic field is sufficiently strong. These results suggest that the magnetic field str ucture has a crucial effect on magnetic braking.