Nonaxisymmetric magnetic field generation in rapidly rotating late-type stars

School of Mathematics, University of Manchester, Manchester M13 9PL, UK e-mail: moss@ma.man.ac.uk

Received: 22 July 2004
Accepted: 31 October 2004

Abstract

Recently the discovery of the “flip-flop” phenomenon, by which a predominant “active” longitude jumps by about , on several rapidly rotating late-type stars has directed attention to the issues surrounding the presence of large-scale nonaxisymmetric magnetic fields in these objects. Here we study nonlinear mean field dynamo models with quasi-cylindrical rotation laws, acting in spherical shells. Stable nonaxisymmetric magnetic fields are found to be generated for a range of parameters and, for certain of these models, jumps in a measure plausibly related to the position of active longitudes are found to occur. In general, nonaxisymmetric fields appear to be easier to generate in thinner dynamo-active regions. However, flip-flops appear to be stronger for intermediate thicknesses of the dynamo-active shells.