Evolved, single, slowly rotating ... but magnetically active. The G8-giant HR 1362 = EK Eridani revisited

Abstract

We rediscuss the unusual case of the slowly rotating late-type giant HR 1362, which exhibits a very unusual high level of magnetic activity. New BVRI photometry from two robotic telescopes from 1991 through 1998 together with previously published photometric data gives a very precise photometric period of 306.9+/-0.4 days. With the aid of high-resolution (R=120,000) optical spectra and the Hipparcos parallax we redetermine the absolute parameters of HR 1362 and find it to be a single G8IV-III star of 14 L_sun and a mass of 1.85 M_sun with T_eff=5125 K, log g=3.25, and solar abundances. Lithium is not significantly different from solar and we obtain log n(Li)=1.14 from a detailed spectrum synthesis including both isotopes at 6708 Angstroms. Vsin i and macroturbulence are determined from fits of disk-integrated models to the observed line profiles as well as their Fourier transforms and are 1.5+/-0.5 km s(-1) \ and ~5 km s(-1) , respectively. The minimum radius from vsin i and P_rot is only then in agreement with the spectral classification and the bolometric luminosity from the Hipparcos parallax if the inclination of the stellar rotation axis is nearly 90°. We concur with the arguments of Stȩpień (\cite{step}) that HR 1362 is an evolved Ap star, and therefore the magnetic field is possibly of galactic origin rather than dynamo generated.