Correcting the record on the analysis of IBEX and STEREO data regarding variations in the neutral interstellar wind

TL;DR

This paper reanalyzes historical and recent data on interstellar wind flow through the heliosphere, addressing previous disputes by confirming the potential for temporal variations while clarifying instrumental and data usage issues.

Contribution

It provides a corrected and updated statistical analysis of interstellar wind data, affirming the possibility of changes over forty years and clarifying the validity of IBEX and STEREO data.

Findings

Temporal variations in interstellar wind are statistically likely.

Constant flow longitude remains a plausible scenario.

IBEX and STEREO data are correctly interpreted and instrumental responses are well understood.

Abstract

The journey of the Sun through space carries the solar system through a dynamic interstellar environment that is presently characterized by Mach 1 motion between the heliosphere and the surrounding interstellar medium (ISM). The interaction between the heliosphere and ISM is an evolving process due to the variable solar wind and to interstellar turbulence. Frisch et al. presented a meta-analysis of the historical data on the interstellar wind flowing through the heliosphere and concluded that temporal changes in the ecliptic longitude of the wind were statistically indicated by the data available in the refereed literature at the time of that writing. Lallement and Bertaux disagree with this result, and suggested, for instance, that a key instrumental response function of IBEX-Lo was incorrect and that the STEREO pickup ion data are unsuitable for diagnosing the flow of interstellar neutrals through the heliosphere. Here we show that temporal variations in the interstellar wind through the heliosphere are consistent with our knowledge of local ISM. The statistical analysis of the historical helium wind data is revisited, and a recent correction of a typographical error in the literature is incorporated into the new fits. With this correction, and including no newer IBEX results, these combined data still indicate that a change in the longitude of the interstellar neutral wind over the past forty years is statistically likely, but that a constant flow longitude is now also statistically possible. It is shown that the IBEX instrumental response function is known, and that the STEREO pickup ion data have been correctly utilized in this analysis.