We present a detailed determination of the astrophysical parameters of the chromospherically active binary star EI Eridani. Our new radial velocities allow to improve the set of orbital elements and reveal long-term variations of the barycentric velocity. A possible third-body orbit with a period of approximately 19 years is presented. Absolute parameters are determined in combination with the Hipparcos parallax. EI Eri's inclination angle of the rotational axis is confined to 56.0 plus/minus 4.5 degrees, its luminosity class IV is confirmed by its radius of 2.37 plus/minus 0.12 R_Sun. A comparison to theoretical stellar evolutionary tracks suggests a mass of 1.09 plus/minus 0.05 M_Sun and an age of approximately 6.15 Gyr. The present investigation is the basis of our long-term Doppler imaging study of its stellar surface.
@article{arxiv.0809.0782,
title = {The chromospherically active binary star EI Eridani I. Absolute dimensions},
author = {A. Washuettl and K. G. Strassmeier and T. Granzer and M. Weber and K. Oláh},
journal= {arXiv preprint arXiv:0809.0782},
year = {2008}
}