Stellar Coronal Abundances. VI. The First Ionization Potential Effect and ξ Bootis A: Solar-like Anomalies at Intermediate-Activity Levels

摘要

Lines from different elements in the Extreme-Ultraviolet Explorer spectra of the corona of the intermediate-activity star ξ Bootis A have been analyzed. Assuming that a photospheric composition for the plasma is responsible for the observed coronal emission, emission measures derived from lines of elements with low first ionization potentials (FIPs) are systematically higher than emission measures derived from lines formed at similar temperatures but due to elements with high FIPs. This problem is alleviated by adopting a "coronal" abundance pattern similar to that which appears to characterize the average solar corona. We interpret these results as evidence that the same FIP-based compositional fractionation mechanism at work in the solar outer atmosphere is also operational in the coronae of significantly more active stars such as ξ Boo A.