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In situ observations of interstellar neutral (ISN) helium atoms by theIBEX-Lo instrument onboard the Interstellar Boundary Explorer (IBEX) missionare used to determine the velocity and temperature of the pristine very localinterstellar medium (VLISM). Most ISN helium atoms penetrating the heliosphere,known as the primary population, originate in the pristine VLISM. As theprimary atoms travel through the outer heliosheath, they charge exchange withHe$^+$ ions in slowed and compressed plasma creating the secondary population.With more than 2.4 million ISN helium atoms sampled by IBEX during ISN seasons2009-2020, we compare the observations with predictions of a parametrized modelof ISN helium transport in the heliosphere. We account for the filtration ofISN helium atoms at the heliospheric boundaries by charge exchange and elasticcollisions. We examine the sensitivity of the ISN helium fluxes to theinterstellar conditions described by the pristine VLISM velocity, temperature,magnetic field, and composition. We show that comprehensive modeling of thefiltration processes is critical for interpreting ISN helium observations, asthe change in the derived VLISM conditions exceeds the statisticaluncertainties when accounting for these effects. The pristine VLISM parametersfound by this analysis are the flow speed (26.6 km s$^{-1}$), inflow directionin ecliptic coordinates (255.7$^\circ$, 5.04$^\circ$), temperature (7350 K),and B-V plane inclination to the ecliptic plane (53.7$^\circ$). The derivedpristine VLISM He$^+$ density is $9.7\times10^3$ cm$^{-3}$. Additionally, weshow a strong correlation between the interstellar plasma density and magneticfield strength deduced from these observations.

Interstellar Conditions Deduced from Interstellar Neutral Helium Observed by IBEX and Global Heliosphere Modeling