Rieger-type cycles on the solar-like star KIC 2852336

¹ Georg-August-Universität, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
² School of Natural Sciences and Medicine, Ilia State University, Cholokashvili ave. 3/5, Tbilisi, Georgia
e-mail: eka.gurgenashvili.1@iliauni.edu.ge
³ E. Kharadze Georgian National Astrophysical Observatory, Mount Kanobili, Georgia
⁴ Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
⁵ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁶ INAF-Osservatorio Astrofisico di Catania, Via S. Sofia, 78, 95123 Catania, Italy

Received: 18 November 2021
Accepted: 24 January 2022

Abstract

Context. A Rieger-type periodicity of 150–180 days (six to seven times the solar rotation period) has been observed in the Sun’s magnetic activity and is probably connected with the internal dynamo layer. Observations of Rieger cycles in other solar-like stars may give us information about the dynamo action throughout stellar evolution.

Aims. We aim to use the Sun as a star analogue to find Rieger cycles on other solar-like stars using Kepler data.

Methods. We analyse the light curve of the Sun-like star KIC 2852336 (with a rotation period of 9.5 days) using wavelet and generalised Lomb-Scargle methods to find periodicities over rotation and Rieger timescales.

Results. Besides the rotation period of 9.5 days, the power spectrum shows a pronounced peak at a period of 61 days (about six times the stellar rotation period) and a less pronounced peak at 40–44 days. These two periods may correspond to Rieger-type cycles and can be explained by the harmonics of magneto-Rossby waves in the stellar dynamo layer. The observed periods and theoretical properties of magneto-Rossby waves lead to the estimation of the dynamo magnetic field strength of 40 kG inside the star.

Conclusions. Rieger-type cycles can be used to probe the dynamo magnetic field in solar-type stars at different phases of evolution. Comparing the rotation period and estimated dynamo field strength of the star KIC 2852336 with the corresponding solar values, we conclude that the ratio Ω/B_D, where Ω is the angular velocity and B_D is the dynamo magnetic field, is the same for the star and the Sun. Therefore, the ratio can be conserved during stellar evolution, which is consistent with earlier observations that younger stars are more active.