ar X iv : a st ro - p h / 98 09 11 8 v 1 9 S ep 1 99 8 A long - duration flare

2RE J0743+224 (BD +23 1799) is a chromospherically active star selected by X-rays and EUV emission detected in the Einstein Slew Survey and ROSAT Wide Field Camara (WFC) all sky survey, and classified as single-lined spectroscopic binary by (Jeffries et al. 1995). We present here high resolution echelle spectroscopic observations of this binary, obtained during a 10 night run 12-21 January 1998 using the 2.1m telescope at McDonald Observatory. These observations reveal it is a double-lined spectroscopic binary. A dramatic increase in the chromospheric emissions (Hα and Ca ii IRT lines) is detected during the observations. Several arguments favor the interpretation of this behavior as an unusual long-duration flare. First the temporal evolution of the event is similar to the observed in other solar and stellar flares, with an initial impulsive phase characterized by a strong increase in the chromospheric lines (the Hα EW change in a factor of 5 in only one day) and thereafter, the line emission decreased gradually over several days. Second, a broad component in the Hα line profile is observed just at the beginning of the event. Third, the detection of the He i D 3 in emission and a filled-in He i λ6678Å. We detect a Li i λ6708Å line enhancement which is clearly related with the temporal evolution of the flare. The maximum Li i enhancement occurs just after the maximum chromospheric emission observed in the flare. We suggest that this Li i is produced by spallation reactions in 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.