Composition of Anomalous Cosmic Rays and Other Ions from Voyager Observations

Abstract

We present energy spectra of eleven cosmic ray elements with energies from rv5 to rv500 MeV/nuc using data obtained from the Voyager spacecraft in the outer heliosphere from early 1993 to the end of 1998. The lowenergy intensity increases observed in all these spectra are consistent with the shapes expected to be exhibited by primarily singly-charged anomalous cosmic rays (ACRs). One of these elements is Na, which is being reported as a member of the ACR component for the first time. We find that the intensity increase below rv 10 Me V /nuc in the Si spectrum in the outer heliosphere is not dominated by re-accelerated solar wind. There is also evidence for a non-ACR component in the energy spectra of Mg, Si, and S observed at 1 AU by the Wind spacecraft below rv5 MeV/nuc. We see evidence in the energy spectra of Ar in both the inner and outer heliosphere for multiply-charged ACRs above rv360 MeV. Using a fit to the ACR intensities with a full-drift, two-dimensional numerical model of the acceleration and propagation of singly-charged ACRs, we present a table of the relative abundances of the seed particles of eleven elements at the solar wind termination shock.