"Elemental Fractionation In Small Solar Energetic Particle Events" by Penny L. Slocum and Joseph R. Dwyer
 

Document Type

Article

Publication Title

The Astrophysical Journal

Abstract

Using the Solar Isotope Spectrometer on the Advanced Composition Explorer (ACE), we have measured the 11.0-21.8 MeV nucleon-1 heavy (Z ≥ 6) element abundances of 39 small solar energetic particle (SEP) events that occurred between 1998 April 3 and 2002 February 26. Using He isotope data from the UltraLow-Energy Isotope Spectrometer on ACE, we have classified the events according to their 0.5-2.0 MeV nucleonˉ¹ ³He/⁴He ratios. We find that their average heavy-element composition is similar to that of either large gradual events or ³He-rich events, depending on their ³He/⁴He ratio. As seen in recent studies of small SEP events, we find that the heavy-element intensities relative to C increase with the ³He/⁴He ratios. The dependence of the heavy-element abundances on first ionization potential (FIP) has been derived, using a model consisting of a power law in Q/M (and Z) times a step function in FIP. We report the magnitude of the FIP factor in each event and find that it varies from ∼2 to 7 with no clear dependence on the ³He/⁴He ratio.

DOI

10.1086/376755

Publication Date

9-1-2003

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