Magnetic activity in the photosphere and chromosphere
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: [sjarvinen;hkorhonen]@aip.de
2 Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
3 Institute of Astronomy, ETH Zentrum, 8092, Zürich, Switzerland e-mail: email@example.com
4 Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
5 Observatory, PO Box 14, University of Helsinki, 00014 Helsinki, Finland
Accepted: 22 June 2007
Context.As a young solar analogue, EK Draconis provides an opportunity to study the magnetic activity of the infant Sun.
Aims.We present three new surface temperature maps of EK Draconis and compare them with previous results obtained from long-term photometry. Furthermore, we determined a set of stellar parameters and compared the determined values with the corresponding solar values.
Methods.Atmospheric parameters were determined by comparing observed and synthetic spectra calculated with stellar atmosphere models. Surface temperature maps were obtained using the Occamian approach inversion technique. The differential rotation of EK Dra was estimated using two different methods.
Results.A detailed model atmosphere analysis of high resolution spectra of EK Dra has yielded a self-consistent set of atmospheric parameters: Teff = 5750 K, log g = 4.5, [M/H] = 0.0, = 1.6 km s-1. The evolutionary models imply that the star is slightly more massive than the Sun and has an age between 30-50 Myr, which agrees with the determined lithium abundance of (Li) = 3.02. Moreover, the atmospheric parameters, as well as the wings of the Ca ii 8662 Å, indicate that the photosphere of EK Dra is very similar to the one of the present Sun, while their chromospheres differ. There also seems to be a correlation between magnetic features seen in the photosphere and chromosphere. The temperature images reveal spots of only 500 K cooler than the quiet photosphere. The mean spot latitude varies with time. The obtained differential rotation is very small, but the sign of it supports solar type differential rotation on EK Dra.
Key words: stars: imaging / stars: activity / stars: starspots / stars: individual: EK Dra
Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.
© ESO, 2007