Detailed Modeling of Neutral Helium in the Heliosphere

An accurate heliospheric neutral test-particle code for primary helium atoms from the interstellar medium (ISM), and for secondary helium atoms born in the outer heliosphere, is coupled to global heliospheric models dominated by hydrogen and protons from the solar wind and the ISM. This coupling allows for ab-initio estimates of charge exchange losses of primary helium and production of secondary helium as they travel from remote boundaries to the inner heliosphere. Taking additionally photoionization into account, a detailed characterization of neutral helium distributions and fluxes in the inner heliosphere is obtained and presented. This region is where neutral helium is observed in detail by, e.g., the IBEX, Ulysses, and IMAP missions.