The Preferential Acceleration of Heavy Nuclei in Solar Flares

Abstract

Several recently reported measurements of the relative abundances of heavy nuclei (Z > 8) accelerated in solar flares have shown a significant enhancement of these nuclei compared with solar photospheric and coronal abundances. We propose a mechanism for the preferential acceleration of heavy nuclei. Our model consists of two acceleration stages: fully stripped ions are first accelerated to suprathermal energies, and subsequently a fraction of these ions are Fermi-accelerated to higher energies. Transport to the Fermi-acceleration region involves electron pickup; injection into Fermi acceleration is rigidity dependent. A consideration of these processes shows that enhancement of the abundance of heavy nuclei can occur. The degree of this enhancement is expected to vary from flare to flare. Thus, this model can aiso account for measurements which have not shown such enhancements.