The influence of the magnetic topology on the wind braking of sun-like stars.
SF2A-2014: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics
Soci´et´e Francaise d’Astronomie et d’Astrophysique
Stellar winds are thought to be the main process responsible for the spin down of main-sequence stars. The extraction of angular momentum by a magnetized wind has been studied for decades, leading to several formulations for the resulting torque. However, previous studies generally consider simple dipole or split monopole stellar magnetic topologies. Here we consider in addition to a dipolar stellar magnetic field, both quadrupolar and octupolar configurations, while also varying the rotation rate and the magnetic field strength. 60 simulations made with a 2.5D, cylindrical and axisymmetric set-up and computed with the PLUTO code were used to find torque formulations for each topology. We further succeed to give a unique law that fits the data for every topology by formulating the torque in terms of the amount of open magnetic flux in the wind. We also show that our formulation can be applied to even more realistic magnetic topologies, with examples of the Sun in its minimum and maximum phase as observed at the Wilcox Solar Observatory, and of a young K-star (TYC-0486-4943-1) whose topology has been obtained by Zeeman-Doppler Imaging (ZDI).
We would like to thank Colin Folsom, Pascal Petit for the magnetic field decomposition coefficients of TYC- 0486-4943-1, J´erome Bouvier and the ANR TOUPIES project which aim to understand the evolution of star?s spin rates, the ERC STARS2 (www.stars2.eu) and CNES support via our Solar Orbiter funding.
pp. 509 - 513