The expected fluxes of secondary ISNs in the VLISM

Abstract:

The Very Local Interstellar Medium (VLISM) is defined as the region around the heliosphere where the interstellar medium is modified or mediated by heliospheric processes and/or material. Previous global models of the heliosphere show that the local interstellar ion flow is deflecting around the heliopause in the VLISM. This flow divergence strongly depends on the shape of the heliopause that in turn is strongly coupled to the local interstellar magnetic field (LISMF). A fraction of the deflected interstellar ions is neutralized by charge exchange with ambient neutral atoms. These neutralized ions are referred to as “secondary interstellar neutrals (ISNs)” and they form enhanced density walls (i.e., H, He, and O walls) in front of the heliopause. Due to different charge exchange rates, these density walls may have different depths and configurations. Due to minimal momentum exchange in charge exchange reactions, the secondary ISNs inherit the kinematic properties of their parent ions. Thus, the observation of secondary ISNs is an essential remote sensing tool to investigate the shape of the heliopause and the configuration of VLISM. In this study, we consider two cases: (1) an axially symmetric flow in the absence of VLISMF and (2) an asymmetric flow by the magnetized plasma. For these two cases, we compute the predicted fluxes of secondary ISNs at the heliopause. In addition, we consider several line-of-sight (LOS) lengths over which the secondary ISNs are accumulated. Comparison of the observations with the predicted fluxes with different LOS lengths can give a fresh insight to the configuration of VLISM. This study can help to determine measurement requirements and instrument concept for the Interstellar Neutral Analyzer on the future Interstellar Probe mission.