Cool Stars 14 - Submitted Abstract # 153 This version created on 05 October 2006 Eclipsed X-ray flares in binary stars Jorge Sanz-Forcada, LAEFF-INTA Fabio Favata, RSSD - European Space Agency Giusi Micela, Observatorio Astronomico di Palermo - INAF The observation of eclipses during X-rays flares taking place in active cool stars binaries allows us to calculate the position and size of the flares. This information can not be derived by analyzing the decay of the flares, a frequently used approach in the literature. We make use of the eclipsing light curve to constrain the set of possible solutions, from the geometrical point of view, in two flares of Algol, and one flare in VW Cep. We make use of a technique developed with the system SV Cam (i~90 deg) and generalize it to binary systems with arbitrary inclination. The method simulates all possible geometrical situations that can produce the times of the four contacts of the eclipse. As an approximation we assume that the emitting region has a spherical shape that remains unchanged during the eclipse. The solutions observed indicate that in two of the three cases the flare can not be polar (lat < 55 deg) and in a third one the flare can be placed either near the pole or at other latitudes. The emitting regions, interpreted as the apex of coronal loops, must have a small size (0.002 - 0.5 R_*) but the loop length could actually be up to 2.8 R_* for one of the Algol flares. These measurements imply a lower limit to the electron density in the emitting region between log n_e (cm^-3) 10.4 and 14.0, and a magnetic field between 70 and 3500 G. ----------------------------------