Effects of the heliospheric interface on the interplanetary Lyman α glow seen at 1 AU from the Sun

Abstract

This work presents multiple scattering computations of interplanetary background line profiles using Angle Dependent Partial Frequency Redistribution to model the scattering process as explained by Quémerais ([CITE]). The density and velocity distribution of hydrogen atoms in the heliosphere was computed using a self-consistent model of the solar wind interaction with the two-component (H atoms and plasma) interstellar plasma (Izmodenov et al. [CITE]). We show that the main difference of the heliospheric interface model as compared to the classical hot model lies in the existence of three populations of H atoms in the heliosphere. These populations are primary interstellar atoms, secondary interstellar atoms created by charge exchange in the outer heliosheath and a hot component (around 150 000 K) created in the inner heliosheath. The two interstellar components provide additional asymmetry in the backscattered Lyα profile at 1 AU, which is not expected from the classical hot model. At the Earth orbit in the upwind direction, the hot component of the backscattered intensity represents less than 5% of the total intensity. It reaches 15% in the downwind direction. Although the heliospheric interface has some effect on the upwind to downwind ratio of total backscattered Lyα intensity, on the apparent velocity and apparent temperature of interplanetary line profiles, they are difficult to discriminate from the results of the variations of the solar parameters. Therefore our following models should include time-dependence effects on the interplanetary hydrogen distribution. Finally, it is concluded that measurements of interplanetary Lyα profiles in the inner heliosphere may serve as a good diagnostic of the heliospheric interface. The existence of a faint hot component in the Lyman α backscattered profiles would serve as a new tool to study the heliospheric interface.