Interstellar Neutral Helium in the Heliosphere from IBEX Observations. VI. The He+ Density and the Ionization State in the Very Local Interstellar Matter

M. Bzowski, A. Czechowski, P. C. Frisch, S. A. Fuselier, A. Galli, J. Grygorczuk, J. Heerikhuisen, M. A. Kubiak, H. Kucharek, D. J. McComas, E. Möbius, N. A. Schwadron, J. Slavin, J. M. Sokół, P. Swaczyna, P. Wurz, E. J. Zirnstein

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Abstract

Interstellar neutral gas atoms penetrate the heliopause and reach 1 au, where they are detected by Interstellar Boundary Explorer (IBEX). The flow of neutral interstellar helium through the perturbed interstellar plasma in the outer heliosheath (OHS) results in the creation of a secondary population of interstellar He atoms, the so-called Warm Breeze, due to charge exchange with perturbed ions. The secondary population brings the imprint of the OHS conditions to the IBEX-Lo instrument. Based on a global simulation of the heliosphere with measurement-based parameters and detailed kinetic simulation of the filtration of He in the OHS, we find the number density of the interstellar He+ population to be (8.98 0.12) 10-3 cm-3. With this, we obtain the absolute density of interstellar H+ as 5.4 10-2 cm-3 and that of electrons as 6.3 10-2 cm-3, with ionization degrees of 0.26 for H and 0.37 for He. The results agree with estimates of the parameters of the Very Local Interstellar Matter obtained from fitting the observed spectra of diffuse interstellar EUV and the soft X-ray background.

Original languageEnglish (US)
Article number60
JournalAstrophysical Journal
Volume882
Issue number1
DOIs
StatePublished - Sep 1 2019

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • ISM: abundances
  • ISM: atoms
  • ISM: clouds
  • ISM: magnetic fields
  • Sun: heliosphere
  • local interstellar matter

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    Bzowski, M., Czechowski, A., Frisch, P. C., Fuselier, S. A., Galli, A., Grygorczuk, J., Heerikhuisen, J., Kubiak, M. A., Kucharek, H., McComas, D. J., Möbius, E., Schwadron, N. A., Slavin, J., Sokół, J. M., Swaczyna, P., Wurz, P., & Zirnstein, E. J. (2019). Interstellar Neutral Helium in the Heliosphere from IBEX Observations. VI. The He+ Density and the Ionization State in the Very Local Interstellar Matter. Astrophysical Journal, 882(1), [60]. https://doi.org/10.3847/1538-4357/ab3462