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Article Dans Une Revue The Astrophysical Journal Année : 2019

Estimating Magnetic Filling Factors from Zeeman–Doppler Magnetograms

Adam J. Finley
  • Fonction : Auteur
Élodie M. Hébrard
  • Fonction : Auteur
Moira M. Jardine
  • Fonction : Auteur
Lisa T. Lehmann
  • Fonction : Auteur
Matthew W. Mengel
  • Fonction : Auteur
Julien Morin
Ian A. Waite
  • Fonction : Auteur
Adam Finley
  • Fonction : Auteur
Moira Jardine
Lisa Lehmann
Aline Vidotto
Ian Waite
  • Fonction : Auteur
  • PersonId : 1009092

Résumé

Low-mass stars are known to have magnetic fields that are believed to be of dynamo origin. Two complementary techniques are principally used to characterize them. Zeeman-Doppler imaging (ZDI) can determine the geometry of the large-scale magnetic field while Zeeman broadening can assess the total unsigned flux including that associated with small-scale structures such as spots. In this work, we study a sample of stars that have been previously mapped with ZDI. We show that the average unsigned magnetic flux follows an activity-rotation relation separating into saturated and unsaturated regimes. We also compare the average photospheric magnetic flux recovered by ZDI, < {B}V> , with that recovered by Zeeman broadening studies, < {B}I> . In line with previous studies, < {B}V> ranges from a few % to ˜20% of < {B}I> . We show that a power-law relationship between < {B}V> and < {B}I> exists and that ZDI recovers a larger fraction of the magnetic flux in more active stars. Using this relation, we improve on previous attempts to estimate filling factors, i.e., the fraction of the stellar surface covered with magnetic field, for stars mapped only with ZDI. Our estimated filling factors follow the well-known activity-rotation relation, which is in agreement with filling factors obtained directly from Zeeman broadening studies. We discuss the possible implications of these results for flux tube expansion above the stellar surface and stellar wind models.

Dates et versions

obspm-02399742 , version 1 (09-12-2019)

Identifiants

Citer

Victor See, Sean P. Matt, Colin P. Folsom, Sudeshna Boro Saikia, Jean-François Donati, et al.. Estimating Magnetic Filling Factors from Zeeman–Doppler Magnetograms. The Astrophysical Journal, 2019, 876 (2), pp.118. ⟨10.3847/1538-4357/ab1096⟩. ⟨obspm-02399742⟩
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