Heliospheric Ly α Absorption in a Split Tail Heliosphere

Abstract:

Neutral hydrogen in the hydrogen wall and heliosheath absorb wavelengths of light near Ly α from nearby stars. Heliospheric models are essential to understand these observations since the observations are an indirect method of probing the the heliosphere. Opher et al. (2015) suggested that the solar magnetic field can collimate the solar wind plasma, resulting in a heliosphere with a split tail. We compare the Ly α predictions made by multi-fluid kinetic-MHD models of Opher et al. 2020, Michael et al. 2020 that present a “Croissant-like” (split tail) shape with long tail models used in Izmodenov et al. 2018. Previous studies have shown that the interstellar magnetic field can affect the distribution of neutral hydrogen in the hydrogen wall just outside the heliosphere. In this study our models use a grid that extends 1500 AU downwind and vary the Interstellar magnetic field strength and direction. The split tail model successfully reproduce the LY α profiles in upwind and sidewind line of sights and have good agreement in downwind line of sights. We comment on the differences between the two MHD models and which directions can be more sensitive to the heliospheric shape as well from the interstellar magnetic field.