Cosmic Ray Source Abundances and the Acceleration of Cosmic Rays
J.S. George, A.C. Cummings, R.A. Leske, R.A. Mewaldt, E.C. Stone
California Institute of Technology, Pasadena, California, USA
M.E. Wiedenbeck, N.E. Yanasak
Jet Propulsion Laboratory, Pasadena, California, USA
W.R. Binns, P.L. Hink, J. Klarmann, M. Lijowski
Washington University, St. Louis, Missouri, USA
E.R. Christian, T.T. von Rosenvinge
NASA / Goddard Space Flight Center, Greenbelt, Maryland, USA
The elemental abundances of galactic cosmic rays (GCRs) observed at
Earth reflect the abundances at the source, and their evolution during
propagation through the Galaxy. Careful modeling of the transport of
cosmic rays through the intervening matter can yield an estimate of
the elemental source composition and help to identify the nature of
the source and acceleration mechanism. It has long been noted that the
GCR elemental source abundances show a fractionation corresponding to
their chemical properties. A similiar effect is observed in the solar
wind and solar energetic particles. The first ionization potential
(FIP) and the condensation temperature (volatility) are two
possibilities for the parameter controlling the fractionation. For
most elements these two quantities are well correlated with each
other. A few elements break the general correlation of FIP and
volatility and the abundances of these may help to distinguish between
models of the pool of material from which the GCRs are
accelerated. The Cosmic Ray Isotope Spectrometer (CRIS) instrument on
ACE has been making measurements of local GCR abundances for about two
years. These new data, combined with a leaky box propagation model,
can provide new insight into the nature of the source and acceleration
of galactic cosmic rays.