Direct Observations of Interstellar H, He, and O by the Interstellar Boundary Explorer

Möbius, E.; Bochsler, P.; Bzowski, M.; Crew, G. B.; Funsten, H. O.; Fuselier, S. A.; Ghielmetti, A. G.; Heirtzler, D.; Izmodenov, Vladislav; Kubiak, M. A.; Kucharek, H.; Lee, M. A.; Leonard, T.; McComas, D. J.; Petersen, L.; Saul, L.; Scheer, J.; Schwadron, N. A.; Witte, M.; Würz, Peter

doi:10.1126/science.1180971

Cited by 134 publications

(127 citation statements)

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“…The simulations were carried out using a specially adapted version of the Warsaw test particle model (Tarnopolski & Bzowski 2009) that was used by Bzowski et al (2012) for analysis of the IBEX observations reported in Möbius et al (2009a) and Bzowski et al (2012). The model is a kinetic test-particle code equivalent to the hot-model of interstellar gas, with a finite temperature and time-and latitude-dependent ionization rate (for details of the hot-model of neutral interstellar gas in the heliosphere see Thomas (1978) or Fahr (1978), for details of the effects of time dependence in the ionization rate on the distribution of interstellar He in the heliosphere (see Ruciński et al 2003).…”

Section: Simulationsmentioning

confidence: 99%

Neutral interstellar He parameters in front of the heliosphere 1994–2007

Bzowski

Kubiak

Hlond

et al. 2014

A&A

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Context. A recent analysis of IBEX measurements of the neutral interstellar He flux showed that the inflow velocity vector is different from the results of an earlier analysis of observations from the GAS instrument onboard Ulysses. A recently published compilation of published results on the helium inflow direction from the past ∼40 years suggested that the inflow direction may be changing with time. Aims. We reanalyzed the old Ulysses data and reprocessed them to increase the accuracy of the instrument pointing to investigate whether the GAS/Ulysses observations, carried out during almost two solar cycles, support the hypothesis that the direction of the interstellar helium inflow is changing. Methods. We employed a similar analysis method as had been used in the analysis of the IBEX data. We sought a parameter set that minimizes the reduced χ 2 , using the Warsaw test-particle model for the interstellar He flux at Ulysses with a state-of-the-art model of neutral He ionization in the heliosphere that precisely reproduces the observation conditions. We also propose a supplementary method of constraining the parameters based on cross-correlations of parameters obtained from an analysis of carefully selected subsets of data. Results. We find that the ecliptic longitude and speed of interstellar He agree very well with the values reported in the original GAS analysis. We find, however, that the temperature is markedly higher. The three-seasons best-fit parameter set is λ = 255.3 • , β = 6 • (J2000), v = 26.0 km s −1 , and T = 7500 K. We do not find evidence that these parameters are varying with time, but their uncertainty range is wider than originally reported. Conclusions. The originally derived parameters of interstellar He from direct sampling on GAS/Ulysses agree well with those currently derived, except for the temperature, which seems to be appreciably higher; this agrees well with interstellar absorption line results. While the results of our analysis agree marginally with the previously reported results from IBEX, the most likely values from the two analyses differ for reasons that are still not understood.

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Section: Simulationsmentioning

confidence: 99%

Neutral interstellar He parameters in front of the heliosphere 1994–2007

Bzowski

Kubiak

Hlond

et al. 2014

A&A

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“…Such a method has recently become available with the launch of the Interstellar Boundary Explorer (IBEX) satellite McComas et al (2009), which owing to its time of flight (TOF) mass spectrometer IBEX-Lo (Fuselier et al 2009), is able to sample Appendices are available in electronic form at http://www.aanda.org neutral interstellar (NIS) H, He, Ne, and O at Earth's orbit (Möbius et al 2009;Bochsler et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Bzowski

Sokół

Kubiak

et al. 2013

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Context. Direct sampling of neutral interstellar (NIS) atoms by the Interstellar Boundary Explorer (IBEX) can potentially provide a complementary method for studying element abundances in the Local Interstellar Cloud (LIC) and processes in the heliosphere interface. Aims. We set the stage for abundance-aimed in-depth analysis of measurements of NIS He, Ne, and O by IBEX and determine systematic differences between abundances derived from various calculation methods and their uncertainties.Methods. Using a model of ionization rates of the NIS species in the heliosphere, based on independent measurements of the solar wind and solar EUV radiation, we developed a time-dependent method of calculating the survival probabilities of NIS atoms from the termination shock (TS) of the solar wind to IBEX. With them, we calculated densities of these species along the Earth's orbit and simulated the fluxes of NIS species as observed by IBEX. We studied pairwise ratios of survival probabilities, densities, and fluxes of NIS species at IBEX to calculate correction factors for inferring the abundances at TS. Results. The analytic method of calculating the survival probabilities gives acceptable results only for He and Ne during low solar activity. For the remaining portions of the solar cycle, and at all times for O, a fully time-dependent model should be used. Electronimpact ionization is surprisingly important for NIS O. Interpreting the IBEX observations using the time-dependent model yields the LIC Ne/O abundance of 0.16 ± 40%. The uncertainty is mostly due to uncertainties in the ionization rates and in the NIS gas flow vector. Conclusions. The Ne/He, O/He, and Ne/O ratios for survival probabilities, local densities, and fluxes scaled to TS systematically differ and thus an analysis based only on survival probabilities or densities is not recommended, except the Ne/O abundance for observations at low solar activity.

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“…IBEX-Lo has eight energy channels that measure ENAs in the interval ∼ 0.01 − 2 keV. IBEX-Lo also has the capability to directly measure the impact of neutral atoms with relatively high densities in the surrounding interstellar cloud, such as H, He, O, and possibly Ne, during certain portions of the yearly orbit (Möbius et al 2009). IBEX-Hi has six energy channels covering ∼ 0.3 − 6 keV.…”

Section: Measurements Of Energetic Neutral Atoms From the Heliospherementioning

confidence: 99%

“…These directly detected ISNs create peaks in count rates in the IBEX-Lo sky-maps, at element-specific orbits where the required energy boost is sufficient (e.g. Figure 1 in Möbius et al 2009). Interstellar H and He create pronounced features in the IBEX-Lo maps at 0.015 keV and 0.11 keV, and the weaker O enhancement is visible at 0.6 keV.…”

Section: Measuring the Flow Of Interstellar Neutrals Through The Innementioning

confidence: 99%

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The Interstellar Boundary Explorer (IBEX):

Frisch

McComas

2010

Space Sci Rev

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The Interstellar Boundary Explorer (IBEX) mission is exploring the frontiers of the heliosphere where energetic neutral atoms (ENAs) are formed from charge exchange between interstellar neutral hydrogen atoms and solar wind ions and pickup ions. The geography of this frontier is dominated by an unexpected nearly complete arc of ENA emission, now known as the IBEX 'Ribbon'. While there is no consensus agreement on the Ribbon formation mechanism, it seems certain this feature is seen for sightlines that are perpendicular to the interstellar magnetic field as it drapes over the heliosphere. At the lowest energies, IBEX also measures the flow of interstellar H, He, and O atoms through the inner heliosphere. The asymmetric oxygen profile suggests that a secondary flow of oxygen is present, such as would be expected if some fraction of oxygen is lost through charge exchange in the heliosheath regions. The detailed spectra characterized by the ENAs provide time-tagged samples of the energy distributions of the underlying ion distributions, and provide a wealth of information about the outer heliosphere regions, and beyond.

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Direct Observations of Interstellar H, He, and O by the Interstellar Boundary Explorer

Cited by 134 publications

References 22 publications

Neutral interstellar He parameters in front of the heliosphere 1994–2007

Neutral interstellar He parameters in front of the heliosphere 1994–2007

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

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