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Composition of Anomalous Cosmic Rays and Other Heliospheric Ions

Cummings, A. C. and Stone, E. C. and Steenberg, C. D. (2002) Composition of Anomalous Cosmic Rays and Other Heliospheric Ions. Astrophysical Journal, 578 (1). pp. 194-210. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20140226-144958207

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Abstract

Interstellar pickup ions accelerated by the termination shock of the solar wind dominate the anomalous cosmic-ray (ACR) intensities observed by the Voyager spacecraft in the outer heliosphere. Using a two-dimensional acceleration and propagation model, we derive the relative abundances of these interstellar ACRs and determine the mass dependence of the injection/acceleration efficiency for the diffusive acceleration of H^+, He^+, N^+, O^+, and Ne^+. The energy spectra of C, Na, Mg, Si, S, and Ar also exhibit ACR increases at low energies. To interpret these observations, we have developed a new set of ionization rates for 11 neutral atoms, H, He, C, N, O, Ne, Na, Mg, Si, S, and Ar at 1 AU, and a new set of filtration factors relating neutral densities in the local interstellar medium to those at the location of the solar wind termination shock. Using the injection/acceleration efficiencies and the Ar filtration factor, we estimate the density of neutral Ar to be (3.5 ± 1.6) × 10^(-7) cm^(-3) in the local interstellar medium. ACR C may have a significant contribution from interstellar neutral C, but the observed intensities of ACR Na, Mg, Si, and S significantly exceed that expected from interstellar neutrals, providing evidence of another source of pickup ions. One possibility discussed is the recently discovered "inner source" of singly charged ions that is thought to be solar wind atoms desorbed from interplanetary dust grains.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1086/342427 DOIArticle
http://iopscience.iop.org/0004-637X/578/1/194/PublisherArticle
http://dx.doi.org/10.1086/345507ErrataErrata
Additional Information:© 2002 The American Astronomical Society. Received 2002 April 3; accepted 2002 June 20. We thank E. Christian for algorithms to analyze the H and He events that do not stop within the CRS detectors (e.g., ≳ 80 MeV nucleon^(-1)). We thank D. Reames for providing machine-readable intensities for the 1 AU Wind energy spectra. We thank the MIT Space Plasma Group for making IMP 8 data available at their website (ftp://space.- mit.edu/pub/plasma/imp/www/imp.html). SOLAR2000 Research Grade historical irradiances are provided courtesy of W. Kent Tobiska and SpaceWx.com. These historical irradiances have been developed with funding from the NASA UARS, TIMED, and SOHO missions. We appreciate valuable discussions with R. Leske, A. F. Barghouty, N. Schwadron, G. Gloeckler, J. Slavin, P. Frisch, K. Tobiska, G. Ferland, F. Keenan, and P. Stancil. This work was supported by NASA under contract NAS 7-1407.
Group:Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NASANAS 7-1407
Subject Keywords:acceleration of particles; atomic processes; cosmic rays; interplanetary medium; ISM : abundances; ISM : atoms
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2002-01
Record Number:CaltechAUTHORS:20140226-144958207
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140226-144958207
Official Citation:Composition of Anomalous Cosmic Rays and Other Heliospheric Ions A. C. Cummings et al. 2002 ApJ 578 194
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44024
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:01 Mar 2014 22:17
Last Modified:16 Jul 2014 23:29

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