| Issue |
A&A
Volume 464, Number 1, March II 2007
AMBER: Instrument description and first astrophysical results
|
|
|---|---|---|
| Page(s) | 309 - 321 | |
| Section | Stellar atmospheres | |
| DOI | https://doi.org/10.1051/0004-6361:20066449 | |
| Published online | 19 December 2006 | |
Six large coronal X-ray flares observed with Chandra*
Department of Physics, Technion, Haifa 32000, Israel e-mail: [nordon;behar]@physics.technion.ac.il
Received:
26
September
2006
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
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