Cool Stars 14 - Submitted Abstract # 27
This version created on 05 October 2006

Multi-wavelength observations of a giant flare on CN Leo


Carolin Liefke, Hamburger Sternwarte
Juergen H.M.M. Schmitt, Hamburger Sternwarte
Birgit Fuhrmeister, Hamburger Sternwarte 
Ansgar Reiners, Max-Planck-Institut fuer Sonnensystemforschung

We present simultaneous observations of a huge flare on the M5.5 dwarf
CN Leo with VLT/UVES and XMM-Newton, with flux increases by factors up
to 500  in the optical and up to 100  in X-rays and lasting for
approximately 25 minutes.  Photometry with a high time resolution (in
the order of magnitude of 1 sec) is obtained in X-rays, in the U band
with the XMM Optical Monitor operating in Fast Mode, and with the UVES
blue and red exposuremeters.  Time-resolved spectroscopy in X-rays
demonstrates the development of temperature and density of the coronal
flaring plasma.  The behaviour of the chromosphere is simultaneously
traced by various emission lines observed in the blue UVES spectra.
Large increases in the line fluxes are accompanied by significant
enhancements of the continuum level, mainly in the blue part but also
in the red part of the spectra.  The red Ca II triplet and lines of
the hydrogen Paschen series are observed in emission during the flare.
Together with the Balmer lines they trace properties of chromospheric
and transition region plasmas.  Additionally, magnetically sensitive
lines of FeH are suitable to measure flare-related changes in CN Leo's
magnetic field.

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