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Published October 1996 | public
Journal Article

Composition of Anomalous Cosmic Rays and Implications for the Heliosphere

Abstract

We use energy spectra of anomalous cosmic rays (ACRs) measured with the Cosmic Ray instrument on the Voyager 1 and 2 spacecraft during the period 1994/157-313 to determine several parameters of interest to heliospheric studies. We estimate that the strength of the solar wind termination shock is 2.42 (-0.08, +0.04). We determine the composition of ACRs by estimating their differential energy spectra at the shock and find the following abundance ratios: H/He = 5.6 (-0.5, +0.6), C/He = 0.00048 ± 0.00011, N/He = 0.011 ± 0.001, O/He = 0.075 ± 0.006, and Ne/He = 0.0050 ± 0.0004. We correlate our observations with those of pickup ions to deduce that the long-term ionization rate of neutral nitrogen at 1 AU is ~8.3 × 10^(-7) s^(-1) and that the charge-exchange cross section for neutral N and solar wind protons is ~1.0 × 10^(-15) cm^2 at 1.1 keV. We estimate that the neutral C/He ratio in the outer heliosphere is 1.8(-0.7, +0.9) × 10^(-5). We also find that heavy ions are preferentially injected into the acceleration process at the termination shock.

Additional Information

© 1996 Springer. Provided by the NASAAstrophysics Data System. We are grateful to J. T. Hoeksema for providing the tilt observations prior to publication. We thank J. Richardson and J. Belcher for providing the Voyager 2 solar wind speed data. This work was supported by NASA under contract NAS7-918.

Additional details

Created:
August 19, 2023
Modified:
October 26, 2023