Time evolution of magnetic activity cycles in young suns: The curious case of κ Ceti

¹ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: sudeshna.boro.saikia@univie.ac.at
² European Space Agency, European Space Research and Technology Centre, Keplerlaan 1, 2201-AZ Noordwijk, The Netherlands
³ Department of Physics and Space Science, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, ON K7K 0C6, Canada
⁴ Tartu Observatory, University of Tartu, Observatooriumi 1, Tõravere, 61602 Tartumaa, Estonia
⁵ Institute of Astronomy and NAO, Bulgarian Academy of Sciences, 72 Tsarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria
⁶ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁷ Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
⁸ CNRS, Institut de Recherche en Astrophysique et Planetologie, 14 avenue Edouard Belin, 31400 Toulouse, France
⁹ Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
¹⁰ Max Planck Institut für Sonnensystemforschung, Justus von Liebig Weg 3, 37077 Göttingen, Germany
¹¹ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹² University of Southern Queensland, Centre for Astrophysics, Toowoomba, QLD 4350, Australia
¹³ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁴ LUPM-UMR 5299, CNRS & Université Montpellier, place Eugène Bataillon, 34095 Montpellier Cedex 05, France
¹⁵ Department of Physics, Ariel University, Ariel 40700, Israel
¹⁶ School of Physics, Trinity College Dublin, University of Dublin, Dublin-2, Ireland
¹⁷ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 11 June 2021
Accepted: 18 September 2021

Abstract

Context. A detailed investigation of the magnetic properties of young Sun-like stars can provide valuable information on our Sun’s magnetic past and its impact on the early Earth.

Aims. We determine the properties of the moderately rotating young Sun-like star κ Ceti’s magnetic and activity cycles using 50 yr of chromospheric activity data and six epochs of spectropolarimetric observations.

Methods. The chromospheric activity was determined by measuring the flux in the Ca II H and K lines. A generalised Lomb–Scargle periodogram and a wavelet decomposition were used on the chromospheric activity data to establish the associated periodicities. The vector magnetic field of the star was reconstructed using the technique of Zeeman Doppler imaging on the spectropolarimetric observations.

Results. Our period analysis algorithms detect a 3.1 yr chromospheric cycle in addition to the star’s well-known ~6 yr cycle period. Although the two cycle periods have an approximate 1:2 ratio, they exhibit an unusual temporal evolution. Additionally, the spectropolarimetric data analysis shows polarity reversals of the star’s large-scale magnetic field, suggesting a ~10 yr magnetic or Hale cycle.

Conclusions. The unusual evolution of the star’s chromospheric cycles and their lack of a direct correlation with the magnetic cycle establishes κ Ceti as a curious young Sun. Such complex evolution of magnetic activity could be synonymous with moderately active young Suns, which is an evolutionary path that our own Sun could have taken.