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Issue A&A
Volume 446, Number 2, February I 2006
Page(s) 621 - 626
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20054018

A&A 446, 621-626 (2006)
DOI: 10.1051/0004-6361:20054018

On temperature and abundance effects during an X-ray flare on $\sigma$ Geminorum

R. Nordon1, E. Behar2 and M. Güdel3

1  Department of Physics, Technion, Haifa 32000, Israel
    e-mail: nordon@physics.technion.ac.il
2  Department of Physics, Technion, Haifa 32000, Israel
    e-mail: behar@physics.technion.ac.il
3  Paul Scherrer Institut, Würenlingen & Villigen, 5232 Villigen PSI, Switzerland
    e-mail: guedel@astro.phys.ethz.ch

(Recived 9 August 2005 / Accepted 20 September 2005 )

Abstract
We compare quiescent and flare X-ray spectra of the RS CVn binary $\sigma$ Gem obtained with the Chandra and XMM-Newton grating spectrometers. We find that in addition to an overall 25% flux increase, which can be ascribed to variations in the system's quiescence activity over the 15 months that passed between the observations, there is a hot plasma component of $kT_{\rm e} \ga$ 3 keV that arises with the flare. The hot component is manifested primarily by emission from high charge states of Fe and by a vast continuum. The cooler ( $kT_{\rm e}$ $\la 2$ keV) plasma remains undisturbed during the flare. We find no significant variations in the relative abundances during the flare except for a slight decrease (<30%) of O and Ne.


Key words: stars: activity -- stars: corona -- stars: flares -- stars: abundances -- stars: individual: $\sigma$ Geminorum -- X-rays: stars

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