EDP Sciences
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Volume 431, Number 2, February IV 2005
Page(s) 679 - 686
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20041201

A&A 431, 679-686 (2005)
DOI: 10.1051/0004-6361:20041201

Relationship between X-ray and ultraviolet emission of flares from dMe stars observed by XMM-Newton

U. Mitra-Kraev1, L. K. Harra1, M. Güdel2, M. Audard3, G. Branduardi-Raymont1, H. R. M. Kay1, R. Mewe4, A. J. J. Raassen4, 5 and L. van Driel-Gesztelyi1, 6, 7

1  Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
    e-mail: umk@mssl.ucl.ac.uk
2  Paul Scherrer Institut, Würenlingen & Villigen, 5232 Villigen PSI, Switzerland
3  Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA
4  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
5  Astronomical Institute "Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
6  Observatoire de Paris, LESIA, 92195 Meudon, France
7  Konkoly Observatory, 1525 Budapest, Hungary

(Received 30 April 2004 / Accepted 30 September 2004 )

We present simultaneous ultraviolet and X-ray observations of the dMe-type flaring stars AT Mic , AU Mic , EV Lac , UV Cet and YZ CMi obtained with the XMM-Newton observatory. During 40 h of simultaneous observation we identify 13 flares which occurred in both wave bands. For the first time, a correlation between X-ray and ultraviolet flux for stellar flares has been observed. We find power-law relationships between these two wavelength bands for the flare luminosity increase, as well as for flare energies, with power-law exponents between 1 and 2. We also observe a correlation between the ultraviolet flare energy and the X-ray luminosity increase, which is in agreement with the Neupert effect and demonstrates that chromospheric evaporation is taking place.

Key words: stars: chromospheres -- stars: coronae -- stars: flare -- stars: late-type -- ultraviolet: stars -- X-rays: stars

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© ESO 2005