Magnetic fields on young, moderately rotating Sun-like stars - II. EK Draconis (HD 129333)

Abstract

The magnetic fields, activity and dynamos of young solar-type stars can be empirically studied using time series of spectropolarimetric observations and tomographic imaging techniques such as Doppler imaging and Zeeman-Doppler imaging. In this paper, we use these techniques to study the young Sun-like star EK Draconis (SpType: G1.5V, HD 129333) using ESPaDOnS at the Canada-France-Hawaii Telescope and NARVAL at the T ' elescope Bernard Lyot. This multi-epoch study runs from late 2006 until early 2012. We measure high levels of chromospheric activity indicating an active, and varying, chromosphere. Surface brightness features were constructed for all available epochs. The 2006/2007 and 2008 data show large spot features appearing at intermediate latitudes. However, the 2012 data indicate a distinctive polar spot. We observe a strong, almost unipolar, azimuthal field during all epochs, which is similar to that observed on other Sun-like stars. Using magnetic features, we determined an average equatorial rotational velocity, Omega(eq), of similar to 2.50 +/- 0.08 rad d(-1). High levels of surface differential rotation were measured with an average rotational shear, Delta Omega, of similar to 0.27(-0.26)(+0.24) rad d(-1). During an intensively observed 3-month period, from 2006 December until 2007 February, the magnetic field went from predominantly toroidal (similar to 80 per cent) to a more balanced poloidaltoroidal (similar to 40-60 per cent) field. Although the large-scale magnetic field evolved over the epochs of our observations, no polarity reversals were found in our data.