English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX)mission samples interstellar neutral (ISN) helium atoms penetrating theheliosphere from the very local interstellar medium (VLISM). In this study, weanalyze the IBEX-Lo ISN helium observations covering a complete solar cycle,from 2009 through 2020 using a comprehensive uncertainty analysis includingstatistical and systematic sources.W e employ the Warsaw Test Particle Model tosimulate ISN helium fluxes at IBEX, which are subsequently compared with theobserved count rate in the three lowest energy steps of IBEX-Lo. The $\chi^2$analysis shows that the ISN helium flows from ecliptic$(\lambda,\beta)=(255.59^{\circ}\pm0.23^{\circ}, 5.14^{\circ}\pm0.08^{\circ})$,with speed $v_\text{HP}=25.86\pm0.21$ km s$^{-1}$ and temperature$T_\text{HP}=7450\pm140$ K at the heliopause. Accounting for gravitationalattraction and elastic collisions, the ISN helium speed and temperature in thepristine VLISM far from the heliopause are $v_\text{VLISM}=25.9$ km s$^{-1}$and $T_\text{VLISM}=6150$ K, respectively. The time evolution of the ISN heliumfluxes at 1 au over 12 years suggests significant changes in the IBEX-Lodetection efficiency, higher ionization rates of ISN helium atoms in theheliosphere than assumed in the model, or an additional unaccounted signalsource in the analyzed observations. Nevertheless, we do not find anyindication of the evolution of the derived parameters of ISN helium over theperiod analyzed. Finally, we argue that the continued operation of IBEX-Lo tooverlap with the Interstellar Mapping and Acceleration Probe (IMAP) will bepivotal in tracking possible physical changes in the VLISM.

Very Local Interstellar Medium Revealed by Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX