Authors: H. Islam (University of New Hampshire), F. Rahmanifard (University of New Hampshire), N. Schwadron (University of New Hampshire), E. Möbius (University of New Hampshire), M. Lee (University of New Hampshire)

The Interstellar Boundary Explorer carries the IBEX-Lo instrument that measures inflowing interstellar neutral atoms (H, He, Ne, O) and has made fundamental advancements in our understanding of local interstellar flow parameters. The fixed orientation of IBEX-Lo viewing, roughly perpendicular to the radial direction,  leads to a degeneracy in the determination of the interstellar flow parameters.  This degeneracy is expressed in terms of the interstellar neutral (ISN) flow speed, temperature, and inflow latitude as a function inflow longitude, referred to as the IBEX 4D parameter tube. Observation of the longitude of maximum flux at 1 au (is a key observable that defines the parameter tube orientation. Several studies have attempted to break the parameter tube degeneracy. However, the presence of H, He secondary populations, and other species (neon, and oxygen) introduce additional systematic uncertainties into the measurement of these parameters.

In this study we estimate the parameters of Interstellar Helium by comparing the observed rates  with rates obtain from an analytical Model developed by Marty Lee et al. (2016). The count rate is calculated by estimating local distribution function of the neutral interstellar helium gas followed by several integration. The count rates for primary and secondary population are considered simultaneously and compared with the observation. This is the first study where we  analyze  the simultaneous effect of primary and secondary population  in a chi-square minimization without assumptions about primary or secondary population parameters.