The XMM-Newton view of stellar coronae: High-resolution X-ray spectroscopy of Capella

Abstract

We present the high-resolution RGS X-ray spectrum of the stellar binary Capella observed by the XMM-Newton satellite. A multi-thermal approach has first been applied to fit the data and derive elemental abundances. Using the latter, the emission measure distribution has been reconstructed using a Chebychev polynomial fit. Its shape is found to display a sharp peak around 7 MK, consistent with previous EUVE and ASCA results. A smaller but significant amount of emission measure is required around 1.8 MK in order to explain the Ovii He-like triplet and the Cvi Lyα line. We have applied the temperature diagnostics of dielectronic recombination satellite lines to the He-like Ovii triplet to constrain the cool plasma temperature, and have obtained a lower limit consistent with the global reconstruction of the emission measure distribution. We have used line ratios from the forbidden, intercombination, and resonance lines of the Ovii triplet to derive an average density for the cool coronal plasma ( cm-3). Implications for the coronal structure of Capella are discussed.