Cool Stars 14 - Submitted Abstract # 130
This version created on 05 October 2006

Weak X-ray flares on the BY Dra-type binary star CC Eri


Ines Crespo-Chacon, Universidad Complutense de Madrid
Giuseppina Micela, INAF - Osservatorio Astronomico di Palermo
Marilena Caramazza, Universita di Palermo & INAF - Osservatorio Astronomico di Palermo
Fabio Reale, Universita di Palermo
Javier Lopez-Santiago, INAF - Osservatorio Astronomico di Palermo
Ignazio Pillitteri, Universita di Palermo

We present the results of a detailed study of a XMM-Newton observation
of the very active BY Dra-type binary star CC Eri.  Data from the most
sensitive soft X-ray detector presently available - the EPIC-PN CCD
camera - were analysed.  The observation lasted 36.7 ks (0.27 times
the orbital period of CC Eri).  A large X-ray variability was found in
the light curve.  Comparison between the cumulative distribution
function of the observed counts and those simulated for a constant
source allowed us to discern real stellar variability from statistical
fluctuations.  Thus, we detected three flares weaker than those
typically observed (with flux change of factors 1.3-1.8 and duration
between 1.6 and 6.7 ks) together with smoother variations with no
clear flare activity.  A time-resolved study of coronal properties
(temperature, emission measure and abundance) was carried out making
use of the Astrophysical Plasma Emission Code (APEC).  A 3-T model was
needed to fit the spectra.  For the first time in a star, no clear
temperature variation was found during the observed flares.  However,
the emission measure of the two hottest components, and their ratio,
suffered from great changes.  The slope of the decay path in the
density-temperature diagram allowed us to determine the presence of
sustained heating during the flare decay and to obtain an upper limit
for the length of the flaring loops, as well as constraints on the
magnetic geometry that are in agreement with previous results reported
for some UV Ceti-type stars.

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