Lithium and magnetic fields in giants. HD 232862 : a magnetic and lithium-rich giant star

摘要

We report the detection of an unusually high lithium content in HD 232862, afield giant classified as a G8II star, and hosting a magnetic field. With thespectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected highresolution and high signal-to-noise spectra of three giants : HD 232862, KU Pegand HD 21018. From spectral synthesis we have inferred stellar parameters andmeasured lithium abundances that we have compared to predictions fromevolutionary models. We have also analysed Stokes V signatures, looking for amagnetic field on these giants. HD 232862, presents a very high abundance oflithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically valueexpected at this spectral type and for this luminosity class (i.e, G8II). Theevolutionary stage of HD 232862 has been precised, and it suggests a mass inthe lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0solar mass, at the bottom of the Red Giant Branch. Besides, a time variableStokes V signature has been detected in the data of HD 232862 and KU Peg,pointing to the presence of a magnetic field at the surface of these tworapidly rotating active stars.