Six large coronal X-ray flares observed with Chandra*
Department of Physics, Technion, Haifa 32000, Israel e-mail: [nordon;behar]@physics.technion.ac.il
Accepted: 4 December 2006
Aims.A study of the six largest coronal X-ray flares in the Chandra archive is presented. The flares were observed on II Peg, OU And, Algol, HR 1099, TZ CrB and CC Eri, all with the High Energy Transmission Grating spectrometer (HETG) and the ACIS detectors.
Methods.We reconstruct an Emission Measure Distribution , using a spectral line analysis method, for flare and quiescence states separately and compare the two. Subsequently, elemental abundances are obtained from the EMD.
Results.We find similar behaviour of the EMD in all flares, namely a large high-T component appears while the low-T ( keV) plasma is mostly unaffected, except for a small rise in the low-T Emission Measure. In five of the six flares we detect a First Ionization Potential (FIP) effect in the flare abundances relative to quiescence. This may contradict previous suggestions that flares are the cause of an inverse FIP effect in highly active coronae.
Key words: stars: activity / stars: corona / stars: flares / stars: abundances / X-rays: stars
© ESO, 2007