Do Non-dipolar Magnetic Fields Contribute to Spin-down Torques?
- Author(s)
- , Victor See, Sean P. Matt, Adam J. Finley, Colin P. Folsom, Sudeshna Boro Saikia, Jean-Francois Donati, Rim Fares, Élodie M. Hébrard, Moira M. Jardine, Sandra V. Jeffers, Stephen C. Marsden, Matthew W. Mengel, Julien Morin, Pascal Petit, Aline A. Vidotto, Ian A. Waite
- 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.
- Organisation(s)
- Department of Astrophysics
- External organisation(s)
- University of Exeter, University of Toulouse, Institut de Recherche en Astrophysique et Planétologie (IRAP), United Arab Emirates University, University of St. Andrews, Georg-August-Universität Göttingen, University of Southern Queensland, University of Montpellier, University of Dublin, Independent researcher
- Journal
- The Astrophysical Journal
- Volume
- 886
- No. of pages
- 15
- ISSN
- 0004-637X
- DOI
- https://doi.org/10.3847/1538-4357/ab46b2
- Publication date
- 11-2019
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103003 Astronomy, 103004 Astrophysics
- Keywords
- ASJC Scopus subject areas
- Astronomy and Astrophysics, Space and Planetary Science
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/547cc11a-ed81-4f24-8e56-160a85675ef4