Preliminary investigation of circumstellar emission and flares in the fast rotating giant FK comae Original Research Article

FK Comae is a star with some very interesting peculiarities in the solar-stellar connection context. This star is a G5 II fast-rotating giant and its origin and extreme (near breakup) rotational velocity remain a puzzle. It is a perfect candidate to study solar-like activity in extreme conditions of low gravity and magnetic configuration. We present time-resolved spectroscopic observations obtained with the ESA-MUSICOS spectrograph at the Isaac Newton Telescope in May 97. One of the most interesting spectral characteristics of this star is the presence of broad emission in the Balmer and Ca II lines. In particular, its Hα emission seems to extend up to several stellar radii and is erratically variable. We present monitoring of this excess emission, interpreted as arising from giant active loop structures and prominences. We detected flares and also continuous micro-flaring events, that can be associated with excitation/recombination of these magnetically confined loops. The emission present in the He i D3 line is also a clear indication of a very active chromosphere and corona. We report on some modelling techniques applied to the circumstellar environment of this star. We also describe a large flare event observed in Hα, Hβ and He i D3.