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Title: THE EFFECT OF MAGNETIC TOPOLOGY ON THERMALLY DRIVEN WIND: TOWARD A GENERAL FORMULATION OF THE BRAKING LAW

Stellar wind is 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. Sixty 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 phases 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.
Authors:
; ; ;  [1] ;  [2]
  1. Laboratoire AIM, DSM/IRFU/SAp, CEA Saclay, F-91191 Gif-sur-Yvette Cedex (France)
  2. Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4SB (United Kingdom)
Publication Date:
OSTI Identifier:
22364626
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 798; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AXIAL SYMMETRY; COMPUTERIZED SIMULATION; CYLINDRICAL CONFIGURATION; DIPOLES; MAGNETIC FIELDS; MAGNETIC FLUX; MAGNETOHYDRODYNAMICS; MASS; OCTUPOLAR CONFIGURATIONS; PLUTO PLANET; ROTATION; SPIN; STELLAR WINDS; SUN; TOPOLOGY; TORQUE; ZEEMAN EFFECT