Can IBEX detect interstellar neutral helium or oxygen from anti-ram directions?

A. Galli, P. Wurz, J. Park, H. Kucharek, E. Möbius, N. A. Schwadron, J. M. Sokół, M. Bzowski, M. A. Kubiak, P. Swaczyna, S. A. Fuselier, D. J. McComas

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


To better constrain the parameters of the interstellar neutral flow, we searched the Interstellar Boundary EXplorer (IBEX)-Lo database for helium and oxygen from the interstellar medium in the anti-ram direction in the three years (2009-2011) with the lowest background rates. We found that IBEX-Lo cannot observe interstellar helium from the anti-ram direction because the helium energy is too low for indirect detection by sputtering off the IBEX-Lo conversion surface. Our results show that this sputtering process has a low energy threshold between 25 and 30 eV, whereas the energy of the incident helium is only 10 eV for these observations. Interstellar oxygen, on the other hand, could in principle be detected in the anti-ram hemisphere, but the expected magnitude of the signal is close to the detection limit imposed by counting statistics and by the magnetospheric foreground.

Original languageEnglish (US)
Article number30
JournalAstrophysical Journal, Supplement Series
Issue number2
StatePublished - Oct 1 2015
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • ISM: atoms
  • ISM: clouds
  • ISM: kinematics and dynamics
  • Sun: heliosphere
  • methods: data analysis
  • solar neighborhood


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