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

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Observations and modelling of stars with near-solar masses in their early phases of evolution are 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 [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 Mꙩ 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.
We would like to thank S.P. Järvinen for providing the data used in Fig 11, Oleg Kochukov (Uppsala University) for his useful comments concerning the effect of the magnetic field on the derived abundances, and the referee, Pascal Petit, whose critical comments led to substantial improvement of the manuscript. HVŞ acknowledges the support by the Scientific and Technological Research Council of Turkey (TÜBİTAK) through the project 1001 - 115F033. DM acknowledges support by the Spanish Ministry of Economy and Competitiveness (MINECO) from project AYA2016-79425- C3-1-P. This work has made use of data from the European Space Agency (ESA) mission. This work has been partially supported by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. Gaia ( data were processed by the Gaia Data Processing and Analysis Consortium (DPAC, dpac/consortium). © 2020 The Authors. Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
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