On magnetic fields, rossby numbers and dynamo action in late-type stars

Abstract

In this paper we give a brief account of our comparisons of predicted and observed trends in the dependence of the magnetic flux, B _s f _s, and the filling factor, f _s on the Rossby number, Ro, in main-sequence late-type stars. A sample of stars with reliable measurements of B _s and f _s has been selected. The surface average magnetic field, B _s f _s, and the fraction of the star covered by this field, the filling factor, f _s, were computed by using a simple dynamo model plus some assumptions on how the field generated at the bottom of the convection zone emerges at the photosphere. The best fits between B _s f _s and f _s with Ro are shown and a possible theoretical basis for the saturation observed at small values of Ro, both in B _s f _s and fs is discussed. Full details of the work summarised here can be found in Montesinos and Jordan (1993).