Radio and X-Ray Emission in Stellar Magnetic Loops

Abstract

In this paper we present a model of a magnetic loop in an RS CVn active star, in which a distribution of nonthermal particles is episodically injected in the local thermal plasma and then evolves in time due to the effect of collision and radiative losses. Preliminary calculations in the simplifying assumption of a uniform source with constant magnetic field have shown that this model can explain the observed characteristics of the flaring and quiescent radio emission of RS CVn stars (Chiuderi Drago & Franciosini 1993). Here we consider a more realistic magnetic configuration, assuming that the source is a dipolar magnetic loop connecting two starspots on the stellar surface. In the evolution of the particle population also the electrons escaping into the loss-cone are taken into account, and in the calculation of the radio spectrum the free-free emission and absorption by the background thermal plasma and the Razin effect are considered. The main parameters of the loop, sunspot dimension and maximum photospheric field, are derived from optical observations, while the thermal plasma density is left as a free parameter. A more detailed description of the model can be found in Franciosini & Chiuderi Drago (1995).