Heavy coronal ions in the heliosphere. I. Global distribution of charge-states of C, N, O, Mg, Si, and S

Abstract

Aims: Our aim is to investigate and study the de-charging of the elements C, N, O, Mg, Si and S-ions, and assess the fluxes of the resulting ENA in the heliosphere.
Methods: The model treats the heavy ions as test particles convected by (and in a particular case also diffusing through) a hydrodynamically calculated background plasma flow from 1 AU to the termination shock (TS), the heliosheath (HS) and finally the heliospheric tail (HT). The ions undergo radiative and dielectronic recombinations, charge exchanges, photo- and electron impact ionizations with plasma particles, interstellar neutral atoms (calculated in a Monte-Carlo model) and solar photons.
Results: Highly-charged heavy coronal ions flowing with the solar wind undergo successive de-ionizations, mainly in the heliosheath, which leads to charge-states much lower than in the supersonic solar wind. If Coulomb scattering is the main ion energy-loss mechanism, the end product of these deionizations are fluxes of ENA of ∼ 1 keV/nucleon originating in the upwind heliosheath that for C, Mg, Si and S may constitute sources of pickup ions (PUI), significantly exceeding the interstellar supply.
Conclusions: Discussed processes result in (i) distinct difference of the ion charge q in the supersonic solar wind (approximately q≥+Z/2, Z = atomic number) compared to that in the HS (approximately 0 ≤ q ≤ +Z/2)); (ii) probable concentration of singly ionized atoms (q = +1) in the heliosheath towards the heliopause (HP) and in the HT; (iii) possible significant production of ENA in the HS offering natural explanation for production of PUI, and - after acceleration at the TS - anomalous cosmic rays (ACR) of species (like C, Mg, Si, S) unable to enter the heliospheric cavity from outside because of their total ionization in the local interstellar medium.

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