Spectral properties of backscattered solar Ly-alpha radiation in the heliosphere: a theoretical search of the heliospheric boundaries effects

TL;DR

This paper investigates how the solar wind's interaction with the interstellar medium influences the spectral properties of backscattered solar Ly-alpha radiation, using a new comprehensive model to reveal differences from simplified models.

Contribution

It introduces a new effective model for interstellar H atom velocity distribution that accounts for boundary and local effects, improving spectral predictions of Ly-alpha radiation.

Findings

New model predicts smaller Ly-alpha intensities than simplified models.

Significant differences in line-widths of backscattered spectra between models.

Line-widths depend on H atom velocity distribution within a few AU from the Sun.

Abstract

We explore imprints of the solar wind interaction with the local interstellar medium on spectral properties of the backscattered solar Ly-alpha radiation. We employ newly developed effective model for the interstellar H atom velocity distribution function in the heliosphere (Katushkina and Izmodenov 2010, 2011). This model takes into account both global effects of H atom perturbations at the heliospheric boundaries and local (i.e. within 10-20 AU from the Sun) effects of the solar ionization, charge exchange, solar gravitation and radiation pressure. Backscattered solar Ly-alpha profiles and their zero, first and second moments were computed at 1 AU for the anti-solar directions of line-of-sight. Then the moments are compared with the moments calculated by using more simplified one-component and two-component hot models. The comparison shows that the Ly-alpha intensities calculated in the frame of new model are somewhat smaller than those calculated by means of the simplified models. Small differences in the first moment (i.e. line-shift) are also observed in the downwind direction. The largest difference between new model and hot models is seen in the second moment of the backscattered Ly-alpha profile. This moment is also called as line-of-sight temperature or line-width of the backscattered spectra. The spectral width depends on the width of the H atom velocity distribution function within few AU from the Sun. We show that the line-widths calculated on the basis of the our model is qualitatively different from those of simplified models.