1994A&A...289..149S

This work presents a new model for the origin of the tilt and twist of the accretion disk around Her X-1. It is based on an asymmetrical, delayed and therefore phase shifted coronal wind which exerts repulsive forces on the disk. The pressure - temperature distribution of the wind and the underlying corona is calculated by solving the energy balance equation under X-ray irradiation from the central neutron star. It results in a double layered hydrostatic corona with the two temperatures of 10⁶K in the lower part and 10^7.5K in the upper one. An approximative solution of the hydrodynamic energy balance equation for the wind region shows that the wind velocity becomes supersonic at about one scale height of the corona. The detailed geometry and density structure above a flat disk are simulated selfconsistently where the radiation transport was done with Monte Carlo methods. Extrapolation to the warped disk shape yields the torque of the wind acting on the accretion disk together with the viscous and the tidal torques. The resulting torque equation was solved where the boundary conditions exclude any torque from the outside forcing an artificial inclination of the disk. - The model is confirmed by observational evidence.