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

U. Mitra-Kraev (1) , Louise K. Harra (1) , Manuel Güdel (2) , M. Audard (3) , G. Branduardi-Raymont (1) , H. R. M. Kay (1) , R. Mewe (4) , A. J. J. Raassen (4) , Lidia van Driel-Gesztelyi (1, 5, 6)

1 UCL - University College of London [London]
2 Paul Scherrer Institute
3 Columbia Astrophysics Laboratory, Columbia University, New York
4 SRON - SRON Netherlands Institute for Space Research
5 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
6 Physique solaire

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.

Domaines: Astrophysique [astro-ph]; Planète et Univers [physics]

U. Mitra-Kraev, Louise K. Harra, Manuel Güdel, M. Audard, G. Branduardi-Raymont, et al.. Relationship between X-ray and ultraviolet emission of flares from dMe stars observed by XMM-Newton. Astronomy and Astrophysics - A&A, 2005, 431, pp.679-686. ⟨10.1051/0004-6361:20041201⟩. ⟨hal-03733313⟩