Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...449..916z&link_type=abstract
Astrophysical Journal v.449, p.916
Astronomy and Astrophysics
Astronomy
27
Acceleration Of Particles, Sun: Abundances, Sun: Flares, Sun: Particle Emission
Scientific paper
A two-stage model for the enrichment of 3He and heavy ions in solar energetic particles is developed. First, current-driven, electrostatic ion cyclotron instabilities are theoretically and numerically investigated for a plasma consisting of H, 4He, and electrons. It is found that H cyclotron waves can be destabilized at frequencies ω≃ 2Ω3He (Ω3He is the cyclotron frequency of 3He) for a wide region of plasma parameters; the dispersion relation is rather insensitive to the 4He-to-H density ratio n4He/nH, and the important parameter here is the electron-to-H temperature ratio Te/Th , which is only required to be ≳ 1.5. The frequencies of unstable 4He cyclotron waves are ω ≃ 1.1Ω4He if n4He/nH ≃ 0.1. Second, the preferential heating of ions by the ion cyclotron waves is studied. It is shown that the H cyclotron waves are very efficient at heating 3He through the second harmonic resonance and are even more efficient at heating heavy ions with Z*j/Aj ≃ 0.43 (Z*j and Aj are the charge state and the mass number of the jth species ion) through the third harmonic resonance. The 4He cyclotron waves can significantly heat heavy ions with Z*j/Aj ≃ 0.28 through the second harmonic resonance. The H and the 4He cyclotron waves are weak at heating H and 4He. These preheated ions can be further accelerated to high energies in the Fermi acceleration process; we estimate the abundance ratios of high energy particles such as 3He/4He, H/4He, and Fe/Si, and show that these abundance ratios agree with observations. Furthermore, if the electron temperature of the background plasma is variable during the period of an 3He-rich event, the high-charge states of heavy ions and the lack of correlation of 3He/4He and Fe/C can also be explained in our model.
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