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EP: Fachverband Extraterrestrische Physik

EP 15: Heliophysics III

EP 15.5: Vortrag

Donnerstag, 2. April 2009, 17:00–17:15, Zahnklinik

An ACR-induced injection into the heliospheric KeV-ion regime leading to ion power laws — •Hans J. Fahr¹, Igor V. Chashei², and Daniel Verscharen¹ — ¹Argelander Institut für Astronomie, Universität Bonn, Auf dem Huegel 71, 53121Bonn — ²Lebedev Physical Institute, Leninskii pr. 53, 117924 Moscow (Russia)

Heliospheric pick-up ions are well known, but their phase-space distribution is a theoretically unsettled problem. How pick-up ions can form suprathermal tails, extending to far above the injection energy, is not yet satifactorily answered. Fermi-2 velocity diffusion theories help to populate such tails, but cannot explain observations of power-laws with an indicated velocity index -5. We prove that such power-laws cannot result as an equilibrium state between suprathermal ions and MHD-turbulences in mutual energy exchange, since too high pick-up ion pressures were required enforcing a shock-free deceleration of the solar wind. Fermi-2 energy diffusion is too inefficient in the outer heliosphere to generate power-law distributions. We show, however, that power-laws beyond the injection threshold are established, if the injection takes place at energies of the order of 100 KeV. Such an injection is due to modulated anomalous cosmic rays (ACR) at the lower end of their spectrum where they are again convected outwards with the solar wind. A calculation of the pick-up ion spectrum under such conditions in fact delivers power-laws with a velocity power index of -4 and distance-independent intensities confirmed by observational results of VOYAGER-1.