The interstellar gas flow through the heliospheric interface region

Abstract

The relative motion of the solar system with respect to the ambient interstellar medium forms a plasma interface region where the eventually subsonic, interstellar and solar wind plasma flows adapt to each other. In this region ahead of the solar system magnetohydrodynamically perturbed plasma flows are formed which, however, can be penetrated by interstellar neutral atoms at their approach towards the inner heliosphere. Thereby the distribution function of neutral interstellar gas species by means of charge exchange processes in the heliosphere attain gas-specific imprints from the perturbed moments in this plasma region. In recent years one has become interested in the influence of this interface plasma on the helium-to-oxygen-to-hydrogen ratios since observational facts from pick-up ion and anomalous cosmic ray data have meanwhile become available shrinking down the inaccuracy in these ratios to fairly low numbers. The aim thus is to study these ratios as they result from alternative forms of interface structures under debate at present and then to identify the best-fitting interface model. The fact is stressed in this article here that a more conrect description of the interface needs a careful consideration of the magnetic fields and the plasma temperature anisotropies which are involved in the actually prevailing counterflow configuration.