Multi-Site Spectroscopy on FK Comae: An Extreme Activity Laboratory

Abstract

FK Comae Berenices is a rapidly rotating G-type active giant star, near break-up. The extreme variability is one of the most striking characteristics of this star. The Balmer lines features are very broad and variable, with clear signs of extended emitting matter and rotational modulation. We attempt to describe here the variability of these line profiles, illustrating it with our results based on data obtained in May 97 at the Isaac Newton Telescope (INT) in La Palma with the ESA-MUSICOS echelle spectrograph. We describe an extraordinary flare event observed at maximum on May 16th in the Balmer, Ha and Hβ, spectral lines and some techniques applied in the study of the evolving flare structure. The total energy loss in Ha is of the order of 10³⁷ erg. We estimate a continuum counterpart of this event of the order of 10³⁹ erg, making this one of the largest flare energies ever observed.