Abstract A new technique to directly detect low energy neutral helium has been developed and successfully used in space for the first time. It makes possible the in-situ measurement of the local angular distribution of the flow of interstellar neutral helium in the inner heliosphere. Based on the transformation of a velocity distribution, using Liouville's theorem, a straightforward model has been developed to determine, from these measurements, the flow parameters of the interstellar helium at infinity. From twelve measurements at radial distances between 1 and 5 AU, average values of the flow parameters were determined, namely: υ ∞ = 26 ± 1 km s −1, downstream direction: λ ∞ = 72 ± 2.4°, β ∞ = −2.5 ± 2.7°, temperature T ∞ = 6700 ± 1500 K. These values are in agreement with results found by completely different methods (such as, backscattered UV-light, pick-up ions), although in detail there are significant differences.


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    Title :

    The Ulysses neutral gas experiment: Determination of the velocity and temperature of the interstellar neutral helium


    Contributors:
    Witte, M. (author) / Rosenbauer, H. (author) / Banaszkiewicz, M. (author) / Fahr, H. (author)

    Published in:

    Advances in Space Research ; 13 , 6 ; 121-130


    Publication date :

    1993-01-01


    Size :

    10 pages




    Type of media :

    Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English





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