Elemental Composition of the Very Local Interstellar Medium as Deduced from Observations of Anomalous Cosmic Rays
We present a new determination of the relative abundances of the interstellar neutral atoms CI, NI, 0 I, and Ar I. These abundances are derived from Voyager observations of the energy spectra of the anomalous cosmic ray- (ACR) component (He, C, N, 0, Ne, and Ar), using a new analysis technique. We find that the abundances of NI, 0 I, and Ar I are in good agreement with solar system abundances, while the abundance of CI is ~1/100 of the solar system value, consistent with the expectation that C is mostly ionized in the local interstellar medium. As we have reported earlier, we find no evidence for charge-changing interactions associated with the heliopause region.
Additional Information© Organizing Committee of the 21st Int. Cosmic Ray Conference. Provided by the NASA Astrophysics Data System. We thank E. Christian for providing the ACR helium spectrum and M. Allen for a compilation of photoionization cross sections. We thank H. Ogawa for a helpful discussion. This work was supported in part by NASA under contract NAS-7-918 and grant NGR-05-002-160..
Published - 1989-20.pdf