Elemental Composition of the Anomalous Cosmic Ray Component

Abstract

We present a new determination of the abundances (normalized to He I and Ne I) of neutral atoms HI, CI, NI, 0I, and ArI in the very local interstellar medium. These abundances are derived from 1994 Voyager 1 observations of the energy spectra of the anomalous cosmic ray (ACR) component. We find that the abundances of NI, 0I, and ArI are in good agreement with solar system abundances, while the abundance of HI is -1/10 and that of CI is -1/80 of the solar system values, respectively. The low HI abundance suggests that H may be partially assimilated into the solar wind or is disfavored in the acceration process. The low CI abundance is consistent with the expectation that C is mostly ionized in the local interstellar medium. We find no evidence for significant charge-changing interactions associated with the heliosheath region or with significant depletion of atoms into grains in the very local interstellar medium.