The chromospherically active binary star EI Eridani: I. Absolute dimensions

Abstract

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 {≈ 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 ° ± 4.5 °, its luminosity class {IV} is confirmed by its radius of {2.37 ± 0.12} R_{⊙}. A comparison to theoretical stellar evolutionary tracks suggests a mass of 1.09 ± 0.05 M_{⊙} and an age of ≈ 6.15 Gyr. The present investigation is the basis of our long-term Doppler imaging study of its stellar surface.