The chromospherically active binary star EI Eridani I. Absolute dimensions

TL;DR

This study precisely determines the physical parameters of the active binary star EI Eridani, revealing orbital variations, possible third-body influence, and stellar characteristics aligned with evolutionary models, supporting ongoing surface imaging research.

Contribution

It provides improved orbital parameters, detects long-term velocity variations, and estimates stellar properties using combined spectroscopic and astrometric data.

Findings

Detection of long-term barycentric velocity variations.

Possible third-body orbit with a 19-year period.

Stellar parameters consistent with evolutionary models.

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 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.