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.

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