Lithium and magnetic fields in giant stars. HD 232 862: a magnetic and lithium-rich giant

Abstract

Aims: We report the detection of an unusually high lithium content in HD 232 862, a field giant classified as a G8II star, and hosting a magnetic field.
Methods: With the spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we collected high resolution and high signal-to-noise spectra of three giants: HD 232 862, KU Peg and HD 21 018. From spectral synthesis we inferred stellar parameters and measured lithium abundances that we compared to predictions from evolutionary models. We also analysed Stokes V signatures, looking for a magnetic field on these giants.
Results: HD 232 862, presents a very high abundance of lithium (A_Li = 2.45 ± 0.25 dex), far in excess of the theoretically value expected at this spectral type and for this luminosity class (i.e., G8II). The evolutionary stage of HD 232 862 was determined, and it suggests a mass in the lower part of the [ 1.0 M_⊙, 3.5 M_⊙] mass interval, likely 1.5-2.0 M_⊙ , at the bottom of the red giant branch. Also, a time variable Stokes V signature was detected in the data of HD 232 862 and KU Peg, pointing to the presence of a magnetic field at the surface of these two rapidly rotating active stars.

Based on spectropolarimetric observations obtained at the Canada-France-Hawaii Telescope (CFHT, operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii), and at the Télescope Bernard Lyot (TBL at Observatoire du Pic du Midi, CNRS and Université de Toulouse, France).