Short-term variability of inner-source pickup ions at 1 AU

SOHO/CELIAS observations

Institut für Experimentelle und Angewandte Physik (IEAP), Christian Albrechts-Universität zu Kiel, Leibnizstrasse 11, 24118 Kiel, Germany
e-mail: berger@physik.uni-kiel.de

Received: 6 October 2014
Accepted: 30 January 2015

Abstract

Context. In 1995 a second extended source of pickup ions in the inner heliosphere was discovered. Since then this so-called inner source has been characterised in many studies, and various scenarios for its nature have been proposed. But to this day, the detailed nature of the inner source is still unknown.

Aims. Although it seems most likely that an interaction of solar wind and dust plays a key role in the production of the inner source pickup ions, available observations have not provided conclusive evidence for any proposed scenario. By analysing the short-term variability of the inner source, we determine a new observational constraint to address the nature of the inner source.

Methods. We used the data set of the charge time-of-flight instrument that operated in 1996 on-board the solar and heliospheric observatory at the first Lagrangian point to analyse inner source O⁺ and C⁺. The unmatched combination of mass per charge resolution, which is sufficient to definitely resolve O⁺ and C⁺, and typical high count rates of about 150 counts per day allowed us to address the short-term variability of the inner source for the first time.

Results. The comparison of the variability of inner-source and solar-wind ions shows that the flux of inner source pickup oxygen and carbon is directly correlated with the flux of solar wind oxygen, and carbon, respectively.

Conclusions. Among the scenarios for the nature of the inner source alone, the scenario of solar-wind neutralisation agrees with this new observational constraint.