E. Möbius, M. A. Popecki, L. M. Kistler, A. B. Galvin, D. Heirtzler, D. Morris Space Science Center and Dept. of Physics, University of New Hampshire, Durham, NH, USA B. Klecker, A. Bogdanov, D. Hovestadt Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
The ionic charge state distributions of solar energetic particle events are determined with ACE SEPICA on an event by event basis, over the time period from launch through the end of 1998. With the large geometric factor of SEPICA the observations are extended to events with very low fluxes and, where possible, even to quiet times. The study is confined to the most abundant species C, O, Ne, Mg, Si and Fe. For Fe mean charge states are observed, which vary between approximately 11, for clearly CME related events, and about 20 for small events that carry signatures of impulsive events. For these events all elements up to Mg, and sometimes Si, appear almost fully ionized. The charge states of all species follow the same trend as that of Fe in their variation from event to event. A comparison of observed mean charge states with those obtained from a model assuming thermal equilibrium conditions shows a general agreement with temperatures ranging from 1.2 - 10 . 106 K. However, noticeable deviations from charge states at a unique temperature for all species are seen for O at high and for Mg at both high and low charge states, which may suggest a different origin for the charge states. A distinct correlation is observed between the charge states and the overabundances of heavy ions w.r.t. O. It remains puzzling that events with substantial deviations from coronal abundances accelerate almost fully stripped ions, which do not lend themselves easily to fractionation processes based on mass and charge.