A magnetospheric model for radio emission from active, late-type binary stars

Abstract

A simple magnetospheric model for active, late-type stars is described which can account for many of the observed radio and X-ray observations of these systems. The model consists of an axisymmetric field which is dipolar inside a restricted range of polar angles and which is radial everywhere else. The closed field line region contains trapped plasma with both thermal and relativistic populations, while the open field lines contain only thermal plasma. The relativistic electrons in the dead zone radiate radio emission, while the thermal electrons generate X-rays. The radio and X-ray luminosity and the circular polarization and radio spectrum are calculated by numerical integration of the radiative transfer equation. The model successfully accounts for many of the observed properties of the radio emission between 1.4 and 5.0 GHz, including luminosity, spectral index, fractional circular polarization, and angular size.