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.