The energy budget of stellar magnetic fields

Wyke Chun Victor See, Moira Mary Jardine, Aline Vidotto, J.-F. Donati, C. P. Folsom, S. Boro Saikia, J. Bouvier, Rim Fares, Scott Gregory, Gaitee Ara Jaffer Hussain, Sandra Victoria Jeffers, S. C. Marsden, J. Morin, C. Moutou, J. D. do Nascimento, P. Petit, L. Rosén, I. A. Waite

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51 Citations (Scopus)


Spectropolarimetric observations have been used to map stellar magnetic fields, many of which display strong bands of azimuthal fields that are toroidal. A number of explanations have been proposed to explain how such fields might be generated though none are definitive. In this paper, we examine the toroidal fields of a sample of 55 stars with magnetic maps, with masses in the range 0.1–1.5 M⊙. We find that the energy contained in toroidal fields has a power-law dependence on the energy contained in poloidal fields. However the power index is not constant across our sample, with stars less and more massive than 0.5 M⊙ having power indices of 0.72 ± 0.08 and 1.25 ± 0.06, respectively. There is some evidence that these two power laws correspond to stars in the saturated and unsaturated regimes of the rotation-activity relation. Additionally, our sample shows that strong toroidal fields must be generated axisymmetrically. The latitudes at which these bands appear depend on the stellar rotation period with fast rotators displaying higher latitude bands than slow rotators. The results in this paper present new constraints for future dynamo studies.

Original languageEnglish
Pages (from-to)4301-4310
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date17 Sept 2015
Publication statusPublished - 11 Nov 2015


  • Techniques: polarimetric
  • Stars: activity
  • Stars: magnetic field
  • Stars: rotation


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