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Astron. Astrophys. 335, 724-732 (1998)

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Extreme-ultraviolet diagnostics of pick-up ions in regions close to the solar corona

I. Feasibility of new observations

Hans-Jörg Fahr, Horst Fichtner and Horst Scherer

Institut für Astrophysik und Extraterrestrische Forschung der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

Received 22 December 1997 / Accepted 26 March 1998


Recent investigations of pick-up ion data obtained with the AMPTE and the Ulysses spacecraft resulted in the discovery that, in contrast to previous expectation, pick-up ion velocity distribution can be anisotropic. Such anisotropy results from a smaller efficiency of pitch-angle scattering than usually assumed and translates into a larger scattering mean free paths than previously attributed to these particles. We demonstrate that existing and upcoming in-situ observations can be substantially supplemented by Earth-bound observations of the extreme-ultraviolet resonance glow of pick-up ions in the vicinity of the sun. The proposed observations, in combination with a theory of ions being picked-up by the heliospheric magnetic field close to the sun will not only allow us to obtain information about the anisotropy of the pick-up ion velocity distributions, but also to deepen our understanding of the physics of the accelerated solar wind and of the pick-up process of ions in this innermost region of the heliosphere not yet well explored.

Key words: plasmas – methods: observational – Sun: corona – Sun: UV radiation – interplanetary medium

Send offprint requests to: Hans-Jörg Fahr

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© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998