Simultaneous ROSAT XRT and WFC observations of a sample of active dwarf stars |
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| Authors: | V Tsikoudi B J Kellett J H M M Schmitt |
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| Institution: | Laboratory of Astronomy, Department of Physics, University of Ioannina, Ioannina, Greece;Space Science Department, Rutherford Appleton Laboratory, Chilton OX11 0QX;MPI für Extraterretriche Physik, Garching, Germany |
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| Abstract: | The X-ray observations of the ROSAT -PSPC All-Sky Survey have revealed bright and energetic coronae for a number of late-type main-sequence stars, many of them flare stars. We have detected 31 X-ray flares on 14 stars. A search for simultaneous X-ray and EUV (extreme ultraviolet) flares using ROSAT Wide Field Camera survey data revealed a large number of simultaneous flares. These results indicate that the heating mechanisms of the X-ray and EUV‐emitting regions of the stellar coronae are similar. We find X-ray quiescent variability for nine of the 14 stars and simultaneous X-ray and EUV quiescent variability for seven of these nine stars. These results imply that the stellar coronae are in a continuous state of low-level activity. There are tight linear correlations of X-ray flare luminosity with the 'quiescent' X-ray as well as with the stellar bolometric luminosity. The similarity between the X-ray-to‐EUV quiescent and flare luminosity ratios suggests that the two underlying spectra are also similar. Both are indeed consistent with the previously determined Einstein two-temperature models. We suggest that both the variability and spectral results could indicate that the quiescent emission is composed of a multitude of unresolved flares. |
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| Keywords: | stars: activity stars: flare stars: late-type |
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