EDP Sciences
Free Access
Volume 487, Number 1, August III 2008
Page(s) 293 - 306
Section Stellar atmospheres
DOI https://doi.org/10.1051/0004-6361:200809379
Published online 09 June 2008

A&A 487, 293-306 (2008)
DOI: 10.1051/0004-6361:200809379

Multiwavelength observations of a giant flare on CN Leonis

I. The chromosphere as seen in the optical spectra
B. Fuhrmeister1, C. Liefke1, J. H. M. M. Schmitt1, and A. Reiners2

1  Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
    e-mail: bfuhrmeister@hs.uni-hamburg.de
2  University of Göttingen, Friedrich-Hundt-Platz 1, 37077 Göttingen, Germany

Received 10 January 2008 / Accepted 27 April 2008

Aims. Flares on dM stars contain plasmas at very different temperatures and thus affect a wide wavelength range in the electromagnetic spectrum. While the coronal properties of flares are studied best in X-rays, the chromosphere of the star is observed best in the optical and ultraviolet ranges. Therefore, multiwavelength observations are essential to study flare properties throughout the atmosphere of a star.
Methods. We analysed simultaneous observations with UVES/VLT and XMM-Newton of the active M5.5 dwarf CN Leo (Gl 406) exhibiting a major flare. The optical data cover the wavelength range from 3000 to 10 000 Å.
Results. From our optical data, we find an enormous wealth of chromospheric emission lines occurring throughout the spectrum. We identify a total of 1143 emission lines, out of which 154 are located in the red arm, increasing the number of observed emission lines in this red wavelength range by about a factor of 10. Here we present an emission line list and a spectral atlas. We also find line asymmetries for H I, He I, and Ca II lines. For the last, this is the first observation of asymmetries due to a stellar flare. During the flare onset, there is additional flux found in the blue wing, while in the decay phase, additional flux is found in the red wing. We interpret both features as caused by mass motions. In addition to the lines, the flare manifests itself in the enhancement of the continuum throughout the whole spectrum, inverting the normal slope for the net flare spectrum.

Key words: stars: activity -- stars: flare -- stars: chromospheres -- stars: late-type -- stars: individual: CN Leo

© ESO 2008

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.