Open AccessSimultaneous ROSAT XRT and WFC observations of a sample of active dwarf stars
Author(s) -
Tsikoudi V.,
Kellett B. J.,
Schmitt J. H. M. M.
Publication year - 2000
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2000.03906.x
Subject(s) - physics , astrophysics , rosat , stars , flare , luminosity , astronomy , extreme ultraviolet lithography , flare star , k type main sequence star , t tauri star , galaxy , optics
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.