Do non-dipolar magnetic fields contribute to spin-down torques?
Article
Article Title | Do non-dipolar magnetic fields contribute to spin-down torques? |
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ERA Journal ID | 1057 |
Article Category | Article |
Authors | See, Victor (Author), Matt, Sean P (Author), Finley, Adam J (Author), Folsom, Colin P (Author), Boro Saikia, Sudeshna (Author), Donati, Jean-Francois (Author), Fares, Rim (Author), Hebrard, Elodie M (Author), Jardine, Moira M (Author), Jeffers, Sandra V (Author), Marsden, Stephen C (Author), Mengel, Matthew W (Author), Morin, Julien (Author), Petit, Pascal (Author), Vidotto, Aline A (Author) and Waite, Ian W (Author) |
Journal Title | The Astrophysical Journal: an international review of astronomy and astronomical physics |
Journal Citation | 886 (2), pp. 1-15 |
Article Number | 120 |
Number of Pages | 15 |
Year | 2019 |
Publisher | IOP Publishing |
Place of Publication | United States |
ISSN | 0004-637X |
1538-4357 | |
Digital Object Identifier (DOI) | https://doi.org/10.3847/1538-4357/ab46b2 |
Web Address (URL) | https://iopscience.iop.org/article/10.3847/1538-4357/ab46b2 |
Abstract | Main-sequence low-mass stars are known to spin down as a consequence of their magnetized stellar winds. However, estimating the precise rate of this spin-down is an open problem. The mass-loss rate, angular momentum loss rate, and magnetic field properties of low-mass stars are fundamentally linked, making this a challenging task. Of particular interest is the stellar magnetic field geometry. In this work, we consider whether non-dipolar field modes contribute significantly to the spin-down of low-mass stars. We do this using a sample of stars that have all been previously mapped with Zeeman–Doppler imaging. For a given star, as long as its mass-loss rate is below some critical mass-loss rate, only the dipolar fields contribute to its spin-down torque. However, if it has a larger mass-loss rate, higher-order modes need to be considered. For each star, we calculate this critical mass-loss rate, which is a simple function of the field geometry. Additionally, we use two methods of estimating mass-loss rates for our sample of stars. In the majority of cases, we find that the estimated mass-loss rates do not exceed the critical mass-loss rate; hence, the dipolar magnetic field alone is sufficient to determine the spin-down torque. However, we find some evidence that, at large Rossby numbers, non-dipolar modes may start to contribute. |
Keywords | magnetohydrodynamics (MHD) – stars: evolution – stars: low-mass – stars: magnetic field – stars: rotation – stars: winds, outflows |
ANZSRC Field of Research 2020 | 510109. Stellar astronomy and planetary systems |
Byline Affiliations | University of Exeter, United Kingdom |
University of Toulouse, France | |
University of Vienna, Austria | |
United Arab Emirates University, United Arab Emirates | |
University of St Andrews, United Kingdom | |
University of Gottingen, Germany | |
Centre for Astrophysics | |
Montpellier Universe and Particles Laboratory, France | |
University of Dublin, Ireland | |
Institution of Origin | University of Southern Queensland |
https://research.usq.edu.au/item/q5892/do-non-dipolar-magnetic-fields-contribute-to-spin-down-torques
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