The crucial role of surface magnetic fields for stellar dynamos: ϵ Eridani, 61 Cygni A, and the Sun

Author(s)

S. V. Jeffers, R. H. Cameron, S. C. Marsden, S. Boro Saikia, C. P. Folsom, M. M. Jardine, J. Morin, P. Petit, V. See, A. A. Vidotto, U. Wolter, M. Mittag

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 ϵ Eridani.

Our results show that 61 Cygni A follows the Solar dynamo with a regular

cycle at all wavelengths, while ϵ 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 ϵ Eridani, we show

that the two chromospheric cycle periods, of ∼3 and ∼13 years,

correspond to two superimposed magnetic cycles.

 

The spectropolarimetic data are available from the Polarbase data

archive: polarbase.irap.omp.eu.

Organisation(s)

Department of Astrophysics

External organisation(s)

Max Planck Institute for Solar System Research, University of Southern Queensland, University of Tartu, University of St. Andrews, University of Montpellier, University of Toulouse, Science and Operations Department - Science Division (SCI-SC), University of Exeter, University of Dublin, Leiden University, Universität Hamburg

Journal

Astronomy & Astrophysics

Volume

661

ISSN

0004-6361

DOI

https://doi.org/10.1051/0004-6361/202142202

Publication date

05-2022

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/05b9d4f5-98eb-4dd6-9080-9e2e1270aa9c