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 ν<SUB>max</SUB> = 253 ± 3 μHz in the first observing run and were able to determine a large separation, ∆ν = 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 α<SUP>2</SUP>Ω dynamo cannot be excluded as the possible origin for the observed magnetic field. <P />A table of the radial velocities is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A106">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A106</A> Based on observations made with the Hertzsprung SONG telescope operated on the Spanish Observatorio del Teide on the island of Tenerife by the Aarhus and Copenhagen Universities and by the Instituto de Astrofísica de Canarias.