Elastic collisions of interstellar helium atoms with solar wind protons

Abstract

Relative motion of the Sun with respect to the surrounding local interstellar medium results in entering of interstellar helium atoms into the heliosphere. Current models of helium flowing into the solar system do not include elastic collisions of atoms with solar wind ions. It was predicted in 1986, without quantitative elaboration, that such collisions would enhance wings of directional distributions of helium atom fluxes. This paper focuses on a theoretical treatment of elastic collisions of interstellar He atoms with the solar wind protons resulting in increased wing intensities, called the helium flux halo in contradistinction to the flux core. We concentrate on directional distributions of He atom intensities at 1 AU from the Sun for observers at rest and moving with the Earth and confirm the formation of the flux halo. We show that the collision-produced halo would often dominate He atom intensities at angles larger than 30°-35° from the maximum intensity direction in the flux core. A comparison with direct measurements of interstellar helium atom fluxes is beyond the scope of this paper. Key Points formation of interstellar helium atom flux halocollisional heating of interstellar helium in the heliosphere ©2013. American Geophysical Union. All Rights Reserved.