Detection of Li i enhancement during a long-duration flare in the recenltly discovered X-ray selected, chromospherically active binary 2RE J0743+2 24

We report the detection of a long-duration optical flare in the recenltly discovered, X-ray selected, chromospherically binary 2RE J0743+224. The high resolution echelle spectroscopic observations taken in 12-21th January 1998 exhibit a dramatic increase in the chromospheric emissions (Hα and Ca ii IRT lines) that we interpret as a flare based on: the temporal evolution of the event, the broad component observed in the Hα line profile, the detection of the He i D₃ in emission and a filled-in He i 6678 Angstroms. During these obsevations we detect a Li i 6708 Angstroms line enhancement which is clearly related with the temporal evolution of the flare. The maximum Li i enhancement (20% in EW) occurs just after the maximum chromospheric emission observed in the flare. A significant increase of the (6) Li/(7) Li isotopic ratio is also detected. For all this we suggest that this Li i enhancement is produced by spallation reactions during the flare. This is the first time that such Li i enhancement associate with a stellar flare is reported, and probably the long-duration of this flare is a key factor for this detection. A large fraction of the stellar surface seem to be covered by starspots during the event, as we deduce for the analysis of the TiO 7055 Angstroms band, thus taken into account the Li i is very temperature sensitive, we can not discard that this Li i variations was related the presence of starspots. However, the correlation with the temporal evolution of the flare, the no detection of changes in the other photospheric absorption lines, and the large changes observed in the core of the Li i, as predict the models, argue in favour of the hipothesis that the Li i is produced during the flare.