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Astron. Astrophys. 357, 716-724 (2000)


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Evaluation of solar energetic Fe charge states: effect of proton-impact ionization

L. Kocharov 1, G.A. Kovaltsov 1,2, J. Torsti 1 and V.M. Ostryakov 3

1 Space Research Laboratory, Department of Physics, University of Turku, 20014 Turku, Finland
2 Ioffe Physical-Technical Institute, St.Petersburg 194021, Russia
3 St.Petersburg State Technical University, St.Petersburg 195251, Russia

Received 16 December 1999 / Accepted 3 February 2000

Abstract

We present the energy-dependent rates of ionization and recombination of energetic Fe ions in solar coronal plasma for the energy range from 0.01 to above 100 MeV nucleon-1. For the [FORMULA] MeV n-1 ions, the energy dependencies become essential for both ionization and recombination processes. Ionization of the Fe projectile by ambient protons is important if the Fe energy exceeds typically [FORMULA] MeV n-1. The equilibrium distributions established by the balance between ionization and recombination collisions are calculated for the temperature range [FORMULA] K. We also present numerical calculations of the time-dependent (nonequilibrium) mean charge state at a given energy of the Fe ion. The results are relevant for the interpretation of charge states of the solar energetic ions. Our calculations support the qualitative conclusion that the observed energy-dependent Fe charge states are a result of concurrent acceleration and charge-changing processes. However, the estimated time scales of the processes are shorter than would be expected based on the energy-independent (thermal) charge-changing rates with no proton impact ionization included. The [FORMULA] MeV n-1 Fe charge state observed in the 6-9 November 1997 event and our calculations suggest that the [FORMULA] MeV n-1 ions were accelerated mainly near the Sun, at heliocentric distances [FORMULA].

Key words: Sun: corona – Sun: flares – Sun: particle emission – acceleration of particles

Send offprint requests to: L.Kocharov (leon.kocharov@srl.utu.fi)

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000

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