Interaction of interstellar pick-up ions with the solar wind |
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| Authors: | E Möbius B Klecker D Hovestadt M Scholer |
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| Institution: | (1) Institut für extraterrestrische Physik, Max-Planck-Institut für Physik und Astrophysik, Garching, Germany |
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| Abstract: | The interaction of interstellar pick-up ions with the solar wind is studied by comparing a model for the velocity distribution function of pick-up ions with actual measurements of He+ ions in the solar wind. The model includes the effects of pitch-ang'e diffusion due to interplanetary Alfvén waves, adiabatic deceleration in the expanding solar wind and the radial variation of the source function. It is demonstrated that the scattering mean free path is in the range  0.1 AU and that energy diffusion can be neglected as compared with adiabatic deceleration. The effects of adiabatic focusing, of the radial variation of the neutral density and of a variation of the solar wind velocity with distance from the Sun are investigated. With the correct choice of these parameters we can model the measured energy spectra of the pick-up ions reasonably well. It is shown that the measured differential energy density of the pick-up ions does not vary with the solar wind velocity and the direction of the interplanetary magnetic field for a given local neutral gas density and ionization rate. Therefore, the comparison of the model distributions with the measurements leads to a quantitative determination of the local interstellar gas density.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988. |
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