Heavy coronal ions in the heliosphere*
I. Global distribution of charge-states of C, N, O, Mg, Si, and S
Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw, Poland e-mail: email@example.com
2 Lomonosov Moscow State University, Department of Mechanics and Mathematics & Space Research Institute (IKI) Russian Academy of Sciences, Moscow, Russia
Accepted: 2 December 2009
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.
Key words: Sun: abundances / solar wind / interplanetary medium / ISM: abundances / cosmic rays / atomic processes
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© ESO, 2010