Neutral H density at the termination shock: a consolidation of recent results

TL;DR

This paper consolidates recent measurements of neutral hydrogen density at the termination shock using various data and models, highlighting a novel method and providing a refined density estimate.

Contribution

It introduces a new method for determining H density from pickup ion data and consolidates existing results for improved accuracy.

Findings

H density at termination shock: 0.09 ± 0.022 cm^-3

H density in local interstellar cloud: 0.16 ± 0.04 cm^-3

Validated a novel measurement approach

Abstract

We discuss a consolidation of determinations of the density of neutral interstellar H at the nose of the termination shock carried out with the use of various data sets, techniques, and modeling approaches. In particular, we focus on the determination of this density based on observations of H pickup ions on Ulysses during its aphelion passage through the ecliptic plane. We discuss in greater detail a novel method of determination of the density from these measurements and review the results from its application to actual data. The H density at TS derived from this analysis is equal to 0.087 \pm 0.022 cm-3, and when all relevant determinations are taken into account, the consolidated density is obtained at 0.09 \pm 0.022 cm-3. The density of H in CHISM based on literature values of filtration factor is then calculated at 0.16 \pm 0.04 cm-3.