The XMM-Newton view of stellar coronae: X-ray spectroscopy of the corona of AB Doradus

Abstract

We report results of deep X-ray observations of AB Doradus obtained with the XMM-Newton observatory during its Performance Verification phase. The main objective of the analysis is a study of the spectral variability of coronal plasma in a very active star, including investigations of the variable thermal structure, abundance variations, and possible density changes during flares. AB Dor revealed both quiescent and flaring emission. The RGS spectra show flux changes in lines of highly ionized Fe during the flares, and an increase of the continuum. Elemental abundances increase in the early flare phases, by a factor of three. The quiescent abundances are lower than corresponding solar photospheric values, and tend to increase with increasing first ionization potential, contrary to the behavior in the solar corona. High-resolution spectra show an average density of the cool plasma of ≈ 3 1010 cm-3; this value does not change during the flares. We analyse and model the temporal behavior of heating and cooling, and present model results for one of the flares. We find that magnetic loops with a semilength of the order of 2.5 1010 cm ≈ 0.3 R* are involved.