INTERSTELLAR NEUTRAL HELIUM in the HELIOSPHERE from IBEX OBSERVATIONS. III. Mach NUMBER of the FLOW, VELOCITY VECTOR, and TEMPERATURE from the FIRST SIX YEARS of MEASUREMENTS

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

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Abstract

We analyzed observations of interstellar neutral helium (ISN He) obtained from the Interstellar Boundary Explorer (IBEX) satellite during its first six years of operation. We used a refined version of the ISN He simulation model, presented in the companion paper by Sokół et al. (2015b), along with a sophisticated data correlation and uncertainty system and parameter fitting method, described in the companion paper by Swaczyna et al. We analyzed the entire data set together and the yearly subsets, and found the temperature and velocity vector of ISN He in front of the heliosphere. As seen in the previous studies, the allowable parameters are highly correlated and form a four-dimensional tube in the parameter space. The inflow longitudes obtained from the yearly data subsets show a spread of ∼6°, with the other parameters varying accordingly along the parameter tube, and the minimum χ2 value is larger than expected. We found, however, that the Mach number of the ISN He flow shows very little scatter and is thus very tightly constrained. It is in excellent agreement with the original analysis of ISN He observations from IBEX and recent reanalyses of observations from Ulysses. We identify a possible inaccuracy in the Warm Breeze parameters as the likely cause of the scatter in the ISN He parameters obtained from the yearly subsets, and we suppose that another component may exist in the signal or a process that is not accounted for in the current physical model of ISN He in front of the heliosphere. From our analysis, the inflow velocity vector, temperature, and Mach number of the flow are equal to λISNHe = 255.°8 ± 0.°5, βISNHe = 5.°16 ± 0.°10, TISNHe = 7440 ± 260 K, vISNHe = 25.8 ± 0.4 km s-1, and MISNHe = 5.079 ± 0.028, with uncertainties strongly correlated along the parameter tube.

Original languageEnglish (US)
Article number28
JournalAstrophysical Journal, Supplement Series
Volume220
Issue number2
DOIs
StatePublished - Oct 1 2015
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

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

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    Bzowski, M., Swaczyna, P., Kubiak, M. A., Sokół, J. M., Fuselier, S. A., Galli, A., Heirtzler, D., Kucharek, H., Leonard, T. W., McComas, D. J., Möbius, E., Schwadron, N. A., & Wurz, P. (2015). INTERSTELLAR NEUTRAL HELIUM in the HELIOSPHERE from IBEX OBSERVATIONS. III. Mach NUMBER of the FLOW, VELOCITY VECTOR, and TEMPERATURE from the FIRST SIX YEARS of MEASUREMENTS. Astrophysical Journal, Supplement Series, 220(2), [28]. https://doi.org/10.1088/0067-0049/220/2/28