Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh23c..02w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH23C-02
Physics
2114 Energetic Particles (7514), 7514 Energetic Particles (2114), 7519 Flares
Scientific paper
Ionic charge states can provide important indications of the physical processes and environments associated with the acceleration and transport of solar energetic particles (SEPs). To date, direct measurements of charge states in 3He-rich SEP events have not been made at energies above an MeV/nuc because the combination of high energy and low intensity is not compatible with present measurement technology employing either electrostatic deflection instruments or geomagnetic filtering techniques. Using data from the Solar Isotope Spectrometer (SIS) on ACE, we infer charge states at high energies in a number of 3He-rich events using an indirect technique introduced by Cohen et al. (1999) that is based on mass and charge fractionation as a power law in Q/M. In the best-measured event (20 Aug 2002), the derived Q values are found to have a simple dependence on atomic number, Z, with step increases in the mean number of attached electrons between Z=6 and 7, 8 and 10, and 16 and 18. This pattern, in conjunction with the known masses of the dominant isotopes, is sufficient to account for much of the observed fine structure in elemental abundance enhancement patterns in 3He-rich events relative to solar wind composition. We also have considered the alternative possibility that the fractionation depends on the parameter Q2/M, which affects the time scale for Coulomb losses in the acceleration region. In this case the inferred charge states are close to values found in the corona and solar wind. Comparison with charge states that have been directly measured below ~0.5 MeV/nuc indicates that the fractionation occurs before the particles have been accelerated beyond ~0.1 MeV/nuc and undergone collisional stripping. We present the charge state composition patterns obtained using these two assumptions about the form of the fractionation and then discuss and contrast the implications of the inferred charge states for the origin of 3He-rich SEP events. This work was supported by NASA at Caltech (under grants NAG5-12929 and NNX08AI11G), JPL, and GSFC.
Cohen M. C.
Cummings Alan C.
Leske Richard A.
Mewaldt Richard A.
Stone Edward C.
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