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
Received 16 December 1999 / Accepted 3 February 2000
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 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 MeV n-1. The equilibrium distributions established by the balance between ionization and recombination collisions are calculated for the temperature range 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 MeV n-1 Fe charge state observed in the 6-9 November 1997 event and our calculations suggest that the MeV n-1 ions were accelerated mainly near the Sun, at heliocentric distances .
Key words: Sun: corona Sun: flares Sun: particle emission acceleration of particles
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© European Southern Observatory (ESO) 2000
Online publication: June 5, 2000