Mass Fractionation in Solar Energetic Particles and the Isotopic Composition of the Corona

Abstract

Using the Solar Isotope Spectrometer on the Advanced Composition Explorer, the isotopic composition of solar energetic particles (SEPs) has been measured in 18 large SEP events for abundant elements from C through Ni at energies of tens of Me V /nucleon. Although SEP isotopic composition is found to vary widely from event to event, it is strongly correlated with the elemental composition, suggesting that elemental and isotopic fractionation relative to the coronal source are largely governed by the same processes. Using empirical correlations to correct for the fractionation yields preliminary coronal isotopic abundance values in good agreement with those found in the solar wind, with comparable accuracy.