6533b7d0fe1ef96bd125a32f

RESEARCH PRODUCT

BeppoSAX observation of a large long-duration X-ray flare from UX Arietis

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description

We present two X-ray observations of the RS CVn binary system UX Arietis performed with BeppoSAX in August 1997 and August 1998. A large flare lasting for about 1 day was detected during the rst observation, while the star was quiescent during the second one. Hard X-ray emission up to50 keV was detected in the PDS instrument during the rise and at the peak of the flare. Time-resolved spectroscopy of the flare with the LECS and MECS detectors shows that temperatures as high as 100 MK were reached at the flare peak; such high temperatures are responsible for the high-energy tail seen in the PDS. We conrm that the coronal abundance of UX Ari is strongly subsolar (Z=Z' 0:2 0:3); no signicant variation of the metallicity is observed during the flare. We show that the new LECS response matrices released in January 2000 seem to solve the problem of the high hydrogen column densities systematically found in previous BeppoSAX observations of stellar coronae. We nd in fact for the quiescent spectrum NH =2 :6 10 19 cm 2 , compatible with the expected value; during the flare NH is higher by a factor 5, probably due to the ejection of material. The flare evolution has been analysed using the two-ribbon flare model by Poletto et al. (1988), nding a very good agreement between the model and the observations.