Magnetic activity on the young Sun: A case study of EK Draconis

¹ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Thege út 15-17., 1121 Budapest, Hungary
² HUN-REN CSFK, MTA Centre of Excellence, Konkoly Thege út 15-17., 1121 Budapest, Hungary
³ Eötvös Loránd University, Institute of Physics and Astronomy, Department of Astronomy, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁴ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
⁵ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Institut für Physik und Astronomie, Universität Potsdam, 14476 Potsdam, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 22 August 2025
Accepted: 1 December 2025

Abstract

Context. Young solar analog stars provide key insights into the early stages of stellar evolution, particularly in terms of magnetic activity and rotation. Their rapid rotation, high flaring rate, and enhanced surface activity make them ideal laboratories for testing stellar models or even the solar dynamo.

Aims. Using long-term photometric data, we investigated the cyclic behavior of EK Dra over the past century. We analyzed its short-term activity based on 13 sectors of the Transiting Exoplanet Survey Satellite (TESS). Applying Doppler imaging on high-resolution spectral data, we investigated the short- and long-term spot evolution and surface differential rotation.

Methods. We used a short-term Fourier-transform on 120-year-long archival photometric data in order to search for activity cycles. The short-term space photometry data were fit with an analytic three-spot model, and we hand-selected flares from it to analyze their phase and frequency distribution. Spectral synthesis was used to determine the astrophysical parameters of EK Dra. Using the

iMap

Results. The long-term photometric data reveal a 10.7–12.1-year cycle that was persistently present for 120 years. In the more recent half of the light curve, a 7.3–8.2-year-long signal is also visible. The distribution of the 142 flares in the TESS data shows no correlation with the rotational phase or with the spotted longitudes. The surfaces of the reconstructed Doppler images vary from one rotation to the next, and the lower limit of the spot lifetime lies between 10 and 15 days. Based on the cross-correlation of the Doppler maps, EK Dra has a solar-type differential rotation with a surface shear parameter of α_DR = 0.030 ± 0.008.