Observing and modelling the young solar analogue EK Draconis: starspot distribution, elemental abundances, and evolutionary status

TL;DR

This study combines spectroscopic observations and modelling to analyze the chemical composition, starspot distribution, and evolutionary status of the young solar analogue EK Draconis, providing insights into early stellar dynamo evolution.

Contribution

It presents the first detailed chemical abundance analysis and starspot mapping of EK Draconis, integrating observations with flux emergence simulations to understand its magnetic activity.

Findings

EK Dra has near-solar metallicity with overabundant Li and Ba.

Starspot maps show polar and mid-latitude spots, with some artefacts near the equator.

Simulations agree with observations for high-latitude spots but lack low-latitude features.

Abstract

Observations and modelling of stars with near-solar masses in their early phases of evolution is critical for a better understanding of how dynamos of solar-type stars evolve. We examine the chemical composition and the spot distribution of the pre-main-sequence solar analogue EK Dra. Using spectra from the HERMES Spectrograph (La Palma), we obtain the abundances of 23 elements with respect to the solar ones, which lead to a $[{\rm Fe/H}]=0.03$, with significant overabundance of Li and Ba. The s-process elements Sr, Y, and Ce are marginally overabundant, while Co, Ni, Cu, Zn are marginally deficient compared to solar abundances. The overabundance of Ba is most likely due to the assumption of depth-independent microturbulent velocity. Li abundance is consistent with the age and the other abundances may indicate distinct initial conditions of the pre-stellar nebula. We estimate a mass of 1.04 $M_\odot$ and an age of $27^{+11}_{-8}$\,Myr using various spectroscopic and photometric indicators. We study the surface distribution of dark spots, using 17 spectra collected during 15 nights using the CAFE Spectrograph (Calar Alto). We also conduct flux emergence and transport (FEAT) simulations for EK Dra's parameters and produce 15-day-averaged synoptic maps of the likely starspot distributions. Using Doppler imaging, we reconstruct the surface brightness distributions for the observed spectra and FEAT simulations, which show overall agreement for polar and mid-latitude spots, while in the simulations there is a lack of low-latitude spots compared to the observed image. We find indications that cross-equatorial extensions of mid-latitude spots can be artefacts of the less visible southern-hemisphere activity.