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

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 νmax=253±3μHz in the first observing run and were able to determine a large separation, Δν=16.43±0.22μHz. 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.