Is the efficiency of magnetic braking limited by polar spots?

A. Aibéo, J. M. Ferreira, J. J. G. Lima

Abstract.
The presence of high latitude spots on the surface of rapidly rotating coolstars and the subsequent concentration of magnetic flux near the poles, has lead to the idea that this causes a reduction in the angular momentum carried away by the stellar wind. We apply the analytical MHD wind model of Lima et al. (2001) to determine the influence of the surface flux distribution on the efficiency of the magnetic braking. We determine the angular momentum loss rate for different surface field distributions. Our results clearly show that the density, pressure, velocity and toroidal magnetic field variations are as important as the surface field distribution in determining the angular momentum carried by the wind. For realistic surface rotation profiles, the angular momentum loss increases as the field concentration increases towards the poles, contrary to what one would naively expect!

Star formation in the era of three great observatories
Cambridge, EUA
julho 2005

Tipo: Poster