Cool Stars 14 - Submitted Abstract # 17
This version created on 05 October 2006

Simultaneous V-band and soft X-ray observation of a giant flare on an
M8 dwarf


Beate Stelzer, Osservatorio Astronomico di Palermo
Giuseppina Micela, Osservatorio Astronomico di Palermo
Juergen Schmitt, Hamburger Sternwarte

We present simultaneous V-band and soft X-ray observations of a giant
flare on the M8 star LP412-31.  The data was obtained with
XMM-Newton's Optical Monitor and X-ray CCD camera.  With an increase
of the V band count rate corresponding to ~6 mag, and a similar
amplitude (factor of ~100) of the X-ray lightcurve, this is one of the
most outstanding events throughout the whole history of stellar flare
observations.  Its relevance is further bolstered by the extremely
cool spectral type of the host star.  The flare is of the impulsive
type (decay time shorter than 1 hour), and covers only 20% of the
observing time.  Outside the flare the star was inactive, displaying
constant and very weak X-ray and V band emission.  In contrast, X-ray
observations of most higher-mass active stars have shown continuous
low-level variations, suggesting a power-law distribution of flare
amplitudes.  These differences may indicate qualitative changes in the
character of magnetic activity in the predominantly neutral
atmospheres of the coolest stars and brown dwarfs.  Using timing and
spectral analysis we examine the properties of the emitting plasma in
the context of standard flare models.

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