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

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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.
Original languageEnglish
Article numberA152
Number of pages8
JournalAstronomy and Astrophysics
Early online date25 May 2022
Publication statusPublished - May 2022


  • Stars: activity
  • Stars: individual: 61 Cygni A
  • Stars: individual: ϵ Eridani
  • Stars: magnetic field
  • Sun: activity


Dive into the research topics of 'The crucial role of surface magnetic fields for stellar dynamos: ϵ Eridani, 61 Cygni A, and the Sun'. Together they form a unique fingerprint.

Cite this