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      The Effect of Combined Magnetic Geometries on Thermally Driven Winds I: Interaction of Dipolar and Quadrupolar Fields

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      Date
      2017-08-10
      Author
      Finley, AJ
      Matt, SP
      Date issued
      2017-08-10
      Journal
      Astrophysical Journal
      Type
      Article
      Language
      en
      Publisher
      American Astronomical Society / IOP Publishing
      Rights
      © 2017. The American Astronomical Society. All rights reserved.
      Abstract
      Cool stars with outer convective envelopes are observed to have magnetic fields with a variety of geometries, which on large scales are dominated by a combination of the lowest order fi elds such as the dipole, quadrupole and octupole modes. Magnetised stellar wind outflows are primarily responsible for the loss of angular momentum from these objects during the main sequence. Previous works have shown the reduced effectiveness of the stellar wind braking mechanism with increasingly complex, but singular, magnetic field geometries. In this paper, we quantify the impact of mixed dipolar and quadrupolar fi elds on the spin-down torque using 50 MHD simulations with mixed field, along with 10 of each pure geometries. The simulated winds include a wide range of magnetic fi eld strength and reside in the slow-rotator regime. We fi nd that the stellar wind braking torque from our combined geometry cases are well described by a broken power law behaviour, where the torque scaling with fi eld strength can be predicted by the dipole component alone or the quadrupolar scaling utilising the total field strength. The simulation results can be scaled and apply to all main-sequence cool stars. For Solar parameters, the lowest order component of the fi eld (dipole in this paper) is the most signi ficant in determining the angular momentum loss.
      Funders/Sponsor
      This project has received funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (grant agreement No 682393).
      Description
      This is the author accepted manuscript. The final version is available from the American Astronomical Society via the DOI in this record.
      Citation
      Vol. 845, article 46
      DOI
      https://doi.org/10.3847/1538-4357/aa7fb9
      URI
      http://hdl.handle.net/10871/28700
      ISSN
      1538-4357
      Collections
      • Physics

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