Rotating Oblique Rotator Model

Magnetic fields of the Sun are generally concentrated in small regions characterized by opposite polarities (the so-called "sunspots"), the nature of which change within a short-time scale. The solar magnetic field is not representative of all astrophysical situations. For instance, the magnetic field of some early-type stars and white dwarfs is constant at least over a time scale of decades, but is not symmetric about the star's rotation axis, so that the observer sees a magnetic configuration that changes as the star rotates. The typical rotation period is of the order of 1 day - 1 week. The magnetic morphology is globally organized, and in many i cases it may be approximated by a dipole tilted at a certain angle with respect to the rotation axis. The figure shows an example of how a stellar dipolar field changes as seen from the observer. The presence of a magnetic field is typically detected by studying the nature of the polarization of the spectral lines, which is described by the Stokes parameters: Q and U measure the linear polarization, V the circular polarization. The figure shows how the Stokes profiles of a spectral line appears as the star rotates and presents to the observer different aspects of its magnetic configuration.

Last Revised: 2009 November 2nd