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| Titel |
Inflow Direction of Interstellar Neutrals deduced from Pickup Ion Measurements at 1 AU |
| VerfasserIn |
C. Drews, L. Berger, R. F. Wimmer-Schweingruber |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066329
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| Zusammenfassung |
| The, so called, interstellar pickup ions are born from ionization of the interstellar neutral
background gas by solar UV radiation or charge exchange with solar wind protons. The low
speed of these interstellar particles in respect to the solar wind, forces them - after ionization
- on circular orbits around the magnetic field, which is embedded into the solar
wind. As a result, interstellar pickup ions show very characteristic velocity spectra
with a sharp cut-off at 2-
vSW, once they have been picked up by the solar wind.
Furthermore, the influence by the Sun’s gravitational force and UV radiation results in a
very characteristic angular distribution in the eclitpic plane featuring two distinct
structures, that are both believed to be aligned along the inflow direction of interstellar
matter.
Here we present recent observations of interstellar pickup ions with the Plasma
and Suprathermal Ion Composition instrument (PLASTIC) mounted on the Solar
TErrestrial RElations Observatory A (STEREO A). PLASTIC is a time-of-flight mass
spectrometer, that determines the velocity, mass and charge of incoming ions by measuring
their energy-per-charge, total energy and time-of-flight. STEREO PLASTIC’s big
geometric factor and the unusual prolonged solar minimum allows for the first time
investigation of heavy pickup ions with unprecedented quality. Within the framework of
our analysis we have performed a superposed epoch analysis of four consecutive
STEREO A orbits that allowed us to reveal in-situ the angular distribution of He+ as
well as heavy pickup ions (O+ and Ne+) at 1 AU. By analysing the interstellar
features, namely the interstellar focusing cone and crescent, of the He+, O+ and Ne+
signature, we were able to estimate the inflow direction of interstellar helium as well as
interstellar oxygen and neon. Our measurments revealed an inflow direction of
λHe+ = 77.37°, λO+ = 78.42°, and λNe+ = 77.44°, which deviates from previously
published results, deduced from the position of the He+ focusing cone, by around
2°. |
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