Kinetic parameters of interstellar neutral helium: updated results from the ULYSSES/GAS-instrument

Witte, M.; Banaszkiewicz, M.; Rosenbauer, H.; McMullin, D.

doi:10.1016/j.asr.2003.01.037

Cited by 101 publications

(148 citation statements)

References 11 publications

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“…The Sun is moving compared to the local interstellar with about 25 km s À1 . This results in a stream of low energetic hydrogen and helium neutrals flowing from this direction toward the Sun (Witte et al 2004;Lallement et al 2005). The ENA signal measured by ASPERA-3, on the other hand, seems to increase in integral flux between 30 and 90 , around the anti-apex direction, while a zone with scarcely any signal expands from 180 to 300 .…”

Section: A Spatial Patternmentioning

confidence: 96%

Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary Medium

Galli

Würz

Barabash

et al. 2006

ApJ

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We present an analysis of hydrogen energetic neutral atoms (ENAs) measured by the ASPERA-3 instrument on board Mars Express. We focus on ENAs that have no Martian origin. The energy spectra of these ENAs are all very similar and can be fitted well by a two-component power law. The fluxes, integrated from 0.2 to 10 keV, vary between 5 ; 10 3 and 10 5 cm À2 sr À1 s À1 . We checked for possible sources for these ENAs, but we can rule out a planetary origin, a solar wind origin, contamination by UV from UV bright stars, and contamination by high-energy protons. With our present knowledge we conclude that the heliospheric termination shock is the most plausible source region.

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Section: A Spatial Patternmentioning

confidence: 96%

Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary Medium

Galli

Würz

Barabash

et al. 2006

ApJ

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“…The processing of the original data set was described by Witte et al (1993Witte et al ( , 1996Witte et al ( , 2004, Banaszkiewicz et al (1996), and Witte (2004), and is not repeated here. In the following, we report on the reprocessing of the original data for this study and then detail the preparation of both the original and reprocessed data set for the parameter search we performed.…”

Section: Discussionmentioning

confidence: 99%

“…Based on measurements carried out from mid-1990s to 2001, GAS obtained a J2000 longitude λ = 255.4 • ± 0.5 • , a latitude β = 5.2 • ± 0.2 • , a speed v = 26.3 ± 0.4 km s −1 , and a temperature T = 6300 ± 340 K (Witte 2004; see also Witte et al 1996Witte et al , 2004, while IBEX found λ = 259.2 • or 259.0 • , with an uncertainty of ∼3 • , and β = 5.1 • or 4.9 • , v = 22.8 or 23.5 km s −1 , T = 6200 or 5300−9000 K by Bzowski et al (2012) and by Möbius et al (2012), respectively from measurements carried out in 2009 and 2010. The parameter values obtained from IBEX are tightly correlated with the inflow longitude, and the acceptable parameter ranges form long alleys in the parameter space.…”

Section: Motivationmentioning

confidence: 99%

“…The first end-to-end calibration was performed by Witte et al (2004) using UV-star data obtained during the 1995 season, mainly in NG-mode. In an end-to-end test, the pixel coordinates (in azimuth and elevation) of a star image were transformed into celestial coordinates, and the resulting star position was compared with the well-known astronomical position obtained from a star catalog.…”

Section: Reprocessing the Original Datamentioning

confidence: 99%

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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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“…• [65]. The exact value for the CLIC bulk flow depends on the underlying star sample, since the flow gradually decelerates towards the downwind direction (FS06).…”

Section: Local Ism Data and Distributionmentioning

confidence: 99%

The Sun's journey through the local interstellar medium: the paleoLISM and paleoheliosphere

Frisch

Slavin

2006

Astrophys. Space Sci. Trans.

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Over the recent past, the galactic environment of the Sun has differed substantially from today. Sometime within the past ∼130,000 years, and possibly as recent as ∼56,000 years ago, the Sun entered the tenuous tepid partially ionized interstellar material now flowing past the Sun. Prior to that, the Sun was in the low density interior of the Local Bubble. As the Sun entered the local ISM flow, we passed briefly through an interface region of some type. The low column densities of the cloud now surrounding the solar system indicate that heliosphere boundary conditions will vary from opacity considerations alone as the Sun moves through the cloud. These variations in the interstellar material surrounding the Sun affected the paleoheliosphere.

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Kinetic parameters of interstellar neutral helium: updated results from the ULYSSES/GAS-instrument

Cited by 101 publications

References 11 publications

Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary Medium

Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary Medium

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

The Sun's journey through the local interstellar medium: the paleoLISM and paleoheliosphere

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