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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.

Aims. We observe the nearby, weakly-active single giant, Pollux, in order to directly study and infer the nature of its magnetic field.

Aims.We have studied the active giant V390 Aur using spectropolarimetry to obtain direct and simultaneous measurements of the magnetic field and the activity indicators in order to infer the origin of the activity.

Aims.We report results of a quantitative colorimetric UBVRIanalysis of two flare events on the red dwarf EV Lac. The photometric data were obtained in September 2004, during the multi-site synchronous monitoring from the four observatories in Ukraine, Russia, Greece, and Bulgaria. These observations confirmed the presence of small-scale high-frequency oscillations (HFO) initially detected by Rodonó (1974, A&A, 32, 337) and recently reconfirmed by the authors. Here we discuss the color characteristics of flares and HFO.

Aims. We investigate the long-term evolution of the large-scale photospheric magnetic field geometry of the solar-type star HD?190771. With fundamental parameters very close to those of the Sun except for a shorter rotation period of 8.8?d, HD?190771 provides us with a first insight into the specific impact of the rotation rate in the dynamo generation of magnetic fields in 1?M??stars.Methods. We use circularly polarized, high-resolution spectra obtained with the NARVAL spectropolarimeter (Observatoire du Pic du Midi, France) and compute cross-correlation line profiles with high signal-to-noise ratio to detect polarized Zeeman signatures. From three phase-resolved data sets collected during the summers of 2007, 2008, and 2009, we model the large-scale photospheric magnetic field of the star by means of Zeeman-Doppler imaging and follow its temporal evolution.Results. The comparison of the magnetic maps shows that a polarity reversal of the axisymmetric component of the large-scale magnetic field occurred between 2007 and 2008, this evolution being observed in both the poloidal and toroidal magnetic components. Between 2008 and 2009, another type of global evolution occured, characterized by a sharp decrease of the fraction of magnetic energy stored in the toroidal component. These changes were not accompanied by significant evolution in the total photospheric magnetic energy. Using our spectra to perform radial velocity measurements, we also detect a very low-mass stellar companion to HD?190771.

Aims. We observe the slowly-rotating, active, single giant, EK?Eri, to study and infer the nature of its magnetic field directly.Methods. We used the spectropolarimeter NARVAL at the Telescope Bernard Lyot, Pic du Midi Observatory, and the Least Square Deconvolution method to create high signal-to-noise ratio Stokes?V profiles. We fitted the Stokes?V profiles with a model of the large-scale magnetic field. We studied the classical activity indicators, the Ca?ii?H and K?lines, the Ca?ii?infrared triplet, and H??line.Results. We detected the Stokes V signal of EK Eri securely and measured the longitudinal magnetic field?Blfor seven individual dates spanning 60% of the rotational period. The measured longitudinal magnetic field of EK?Eri reached about 100?G and was as strong as fields observed in RSCVn or FK?Com?type stars: this was found to be extraordinary when compared with the weak fields observed at the surfaces of slowly-rotating MS?stars or any single red giant previously observed with NARVAL. From our modeling, we infer that the mean surface magnetic field is about 270?G, and that the large scale magnetic field is dominated by a poloidal component. This is compatible with expectations for the descendant of a strongly magnetic Ap?star.

Context.EK Eri is one of the most slowly rotating active giants known, and has been proposed to be the descendant of a strongly magnetic Ap star.

Aims.We study the fast rotating M 5 giant EK Boo by means of spectropolarimetry to obtain direct and simultaneous measurements of both the magnetic field and activity indicators, in order to infer the origin of the activity in this fairly evolved giant.