We analyzed observations of interstellar neutral helium ( ISN He ) obtained from the Interstellar Boundary Explorer ( IBEX ) satellite during its first six years of operation .
We used a refined version of the ISN He simulation model , presented in the companion paper by , and a sophisticated data correlation and uncertainty system and parameter fitting method , described in the companion paper by .
We analyzed the entire data set together and the yearly subsets , and found the temperature and velocity vector of ISN He in front of the heliosphere .
As seen in the previous studies , the allowable parameters are highly correlated and form a four-dimensional tube in the parameter space .
The inflow longitudes obtained from the yearly data subsets show a spread of \sim 6 \arcdeg , with the other parameters varying accordingly along the parameter tube , and the minimum \chi ^ { 2 } value is larger than expected .
We found , however , that the Mach number of the ISN He flow shows very little scatter and is thus very tightly constrained .
It is in excellent agreement with the original analysis of ISN He observations from IBEX and recent reanalyses of observations from Ulysses .
We identify a possible inaccuracy in the Warm Breeze parameters as the likely cause of the scatter in the ISN He parameters obtained from the yearly subsets , and we suppose that another component may exist in the signal , or a process that is not accounted for in the current physical model of ISN He in front of the heliosphere .
From our analysis , the inflow velocity vector , temperature , and Mach number of the flow are equal to \lambda _ { \mathrm { ISNHe } } = 255.8 \arcdeg \pm 0.5 \arcdeg , \beta _ { \mathrm { ISNHe } } = 5.16 \arcdeg \pm 0.10 \arcdeg , T _ { \mathrm { ISNHe } } = 7440 \pm 260 K , v _ { \mathrm { ISNHe } } = 25.8 \pm 0.4 km s ^ { -1 } , and M _ { \mathrm { ISNHe } } = 5.079 \pm 0.028 , with uncertainties strongly correlated along the parameter tube .