Neon and oxygen in stellar coronae – a unification with the Sun

Jan Robrade (Hamburger Sternwarte, Germany)

We use high-resolution X-ray spectra from a sample of weakly and moderately active stars to determine their coronal Ne/O abundance ratio and to investigate an enhanced neon abundance as solution of the solar modeling problem. The problem arose from the disagreement between revised solar abundances and helioseismology and  has resulted in a controversy about the true neon abundance of the Sun. We apply two linear combinations of strong emission lines as well as a global-fitting method for each dataset and compare their results. We find a correlation between the Ne/O ratio and stellar activity in the sense that stars with a higher activity level show a higher Ne/O ratio, a trend that is independent of spectral type. The Ne/O abundance ratio decreases from ~0.4 for more active stars down to ~0.2 for low activity stars, i.e. a ratio similar to ‘classical’ solar values. A significantly enhanced neon abundance as the solution to the solar modeling problem is unlikely. From the coronal Ne/O ratios we find no indications of a peculiar position of the Sun among other stars.

Talk presented at the symposium From Atoms to Stars: the impact of Spectroscopy on Astrophysics, 26-28 July 2011, Oxford, UK.

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