1. The crucial role of surface magnetic fields for stellar dynamos: Epsilon Eridani, 61 Cygni A, and the Sun
- Author
-
Jeffers, S., Cameron, R., Marsden, S., Boro Saikia, S., Folsom, C., Jardine, M., Morin, J., Petit, P., See, V., Vidotto, A., Wolter, U., Mittag, M., Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research (MPS), Max-Planck-Gesellschaft, University of Southern Queensland (USQ), University of Vienna, University of Tartu, University of Saint-Andrews, Laboratoire Univers et Particules de Montpellier (LUPM), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM), Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), European Space Research and Technology Centre (ESTEC), Agence Spatiale Européenne = European Space Agency (ESA), Universiteit Leiden, Hamburger Sternwarte, Bcool Collaboration, Science & Technology Facilities Council, European Research Council, and University of St Andrews. School of Physics and Astronomy
- Subjects
Stars: activity ,Stars: magnetic field ,[SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR] ,T-NDAS ,FOS: Physical sciences ,Astronomy and Astrophysics ,Stars: individual: ϵ Eridani ,magnetic field [Stars] ,QC Physics ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Sun: activity ,Physics::Space Physics ,QB Astronomy ,Astrophysics::Solar and Stellar Astrophysics ,activity [Sun] ,Astrophysics::Earth and Planetary Astrophysics ,individual: 61 Cygni A [Stars] ,Stars: individual: 61 Cygni A ,activity [Stars] ,QC ,Solar and Stellar Astrophysics (astro-ph.SR) ,individual: ϵ Eridani [Stars] ,QB - Abstract
Cool main-sequence stars, such as the Sun, have magnetic fields which are generated by an internal dynamo mechanism. In the Sun, the dynamo mechanism produces a balance between the amounts of magnetic flux generated and lost over the Sun's 11-year activity cycle and it is visible in the Sun's different atmospheric layers using multi-wavelength observations. We used the same observational diagnostics, spanning several decades, to probe the emergence of magnetic flux on the two close by, active- and low-mass K dwarfs: 61 Cygni A and Epsilon Eridani. Our results show that 61 Cygni A follows the Solar dynamo with a regular cycle at all wavelengths, while Epsilon Eridani represents a more extreme level of the Solar dynamo, while also showing strong Solar-like characteristics. For the first time we show magnetic butterfly diagrams for stars other than the Sun. For the two K stars and the Sun, the rate at which the toroidal field is generated from surface poloidal field is similar to the rate at which toroidal flux is lost through flux emergence. This suggests that the surface field plays a crucial role in the dynamos of all three stars. Finally, for Epsilon Eridani, we show that the two chromospheric cycle periods, of ~3 and ~13 years, correspond to two superimposed magnetic cycles., Comment: 8 pages, 5 figures: Accepted by A&A
- Published
- 2022