2001A&A...365L.318A

The RS CVn system HR 1099 was observed by XMM-Newton for a time span of 25 days during the commissioning phase. Rotational modulation in the RGS light curve has been detected with maximum flux when the active K1 IV star is in front. Following a quiescent phase of emission, the rise and peak of a large flare were observed. Time-dependent spectroscopy has been performed to derive elemental abundances and their variations during the various stages of the flare. Emission measure distributions have been reconstructed. Two different components are detected: a very hot plasma (up to 100MK) that evolves rapidly, and a stable quiescent plasma. Low first-ionization-potential elemental (such as Fe and Si) abundances increase significantly during the flare, while the abundance of the high-FIP element Ne stays constant at the quiescent value. We report direct detection of a flux increase in the Fe XXIV X-ray lines during a stellar flare.