Heavy Coronal Ions in the Heliosphere: I. Global Distribution of Charge-states of C, N, O, Mg, Si and S

Abstract

Aims: Investigate/Study de-charging of solar wind C, N, O, Mg, Si and S ions and assess fluxes of 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), to heliosheath (HS) and finally to heliospheric tail (HT). The ions undergo radiative and dielectronic recombinations, charge exchanges, photo- and electron impact ionizations with plasma particles, interstellar neutral atoms (calculated on 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, leading 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 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.