Modeling Neutral Hydrogen in the Heliospheric Interface

Observational data of neutral atoms provides us with a 1 AU picture of the neutral atom flux in the heliosphere. The large mean free paths of neutrals allow us to infer properties of their distant source, as well as the properties of the intermediary medium. Energetic neutral hydrogen, for example, travels on almost straight trajectories, so that the particles observed coming from a particular direction were created from energetic protons along that line of sight. Similarly, low energy interstellar atoms are attenuated and deflected as they enter the heliosphere, and this deflection tells us something about the structure of the heliospheric interface. Of course, to infer quantitative features of the global heliosphere from neutral atom observations at 1 AU, we need accurate models that capture the 3D structure of the heliosphere. In this paper we present our MHD-plasma/kinetic-neutral model of the heliospheric interface that uses a Lorentzian distribution function to approximate a suprathermal tail on the solar wind proton distribution due to pick-up ions. We investigate the effect the kappa parameter of the Lorentzian function has on the overall solution and the flux of energetic neutral atoms (ENAs). ENA fluxes are also compared to "pre-IBEX" spacecraft data.