POYNTING JETS AND MHD WINDS FROM RAPIDLY ROTATING MAGNETIZED STARS

Abstract

We discuss results of axisymmetic magnetohydrodynamic theory and simulations of the interaction of a rapidly-rotating, aligned magnetized star with an accretion disk. The disk is considered to have a finite viscosity and magnetic diffusivity. The main parameters of the system are the star’s angular velocity and magnetic moment, and the disk’s viscosity, magnetic diffusivity, and mass accretion rate. We focus on the “propeller” regime where the inner radius of the disk is larger than the corotation radius. We have found two different types of magnetohydrodynamic flows: as a “weak” and “strong” propellers. The strong propellers have a powerful MHD disk wind and a collimated magnetically dominated or Poynting flux outflow from the surface of the star. The weak propellers have only weak outflows. We discuss the time-averaged characteristics of the interaction between the main elements of the system, the star, the disk, the wind from the disk, and the jet from the star. Rates of exchange of mass and angular momentum between the elements of the system are derived as a function of the main parameters. These results are applicable to the early evolution of classical T Tauri stars. They may be also used to explain the variation of angular velocity of neutron stars and cataclysmic variables.