Acoustic oscillations and dynamo action in the G8 sub-giant EK Eridani^⋆,⋆⋆

¹ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia, 78, 95123 Catania, Italy
e-mail: enrico.corsaro@inaf.it, alfio.bonanno@inaf.it
² Institute of Astrophysics, FORTH, 71110 Heraklion, Greece
³ Department of Physics, University of Crete, 70013 Heraklion, Greece
⁴ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁵ School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia

Received: 3 May 2019
Accepted: 2 July 2019

Abstract

We present further evidence of acoustic oscillations in the slowly rotating overactive G8 sub-giant EK Eri. This star was observed with the 1m Hertzsprung SONG telescope at the Observatorio del Teide for two different runs of 8 and 13 nights, respectively, that were separated by about a year. We determined a significant excess of power around ν_max = 253 ± 3 μHz in the first observing run and were able to determine a large separation, Δν = 16.43 ± 0.22 μHz. No significant excess of power was instead detected in a subsequent SONG observing season, as also supported by our analysis of the simultaneous TESS photometric observations. We propose a new amplitude-luminosity relation in order to account for the missing power in the power spectrum. Based on the evolutionary stage of this object, we argue that a standard α²Ω dynamo cannot be excluded as the possible origin for the observed magnetic field.