Models for explaining the observed spatial variation of element abundances -- A review

Details Models for explaining the observed spatial variation of element abundances -- A review Models for explaining the observed spatial variation of element abundances -- A review

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995adspr..15...23h&link_type=abstract

Advances in Space Research (ISSN 0273-1177), vol. 15, no. 7, p. (7)23-(7)32

Astronomy and Astrophysics

Astronomy

27

Abundance, Fractionation, Helium, Ionization Potentials, Solar Corona, Solar Magnetic Field, Spatial Dependencies, Stellar Models, Variations, Astronomical Spectroscopy, Chromosphere, Electric Field Strength, Gravitation, Ions, Neutral Particles, Particle Acceleration, Solar Flares, Solar Maximum Mission, Ultraviolet Astronomy, X Ray Astronomy

Scientific paper

Recent results on the spatial dependence of low and high-FIP (First Ionization Potential) element abundances in the sun, and on the fine structure of this FIP dependence, are briefly discussed. Existing models of FIP fractionation are reviewed. The main models are based on ion-neutral separation in a magnetic field and they differ fundamentally by the nature of the forces -- gravity pressure or electric forces -- acting on the particles -- neutrals or ions -- that cross the lines of force. These models predict an enhancement of low-FIP elements at the coronal level. However, a quantitative prediction of the resulting coronal abundance is still not possible. Abundance enhancements of He-3 and of heavy elements observed in solar energetic particles accelerated in impulsive flares are also quoted, and the most recent particle acceleration theories are briefly presented. In conclusion we emphasize the need to understand the origin of coronal abundances in order to obtain clues on mechanisms for chromospheric formation.

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