 |
| Titel |
Fluxes of energetic neutral helium atoms from the heliosheath and the IBEX Ribbon |
| VerfasserIn |
Pawel Swaczyna, Stan Grzedzielski, Maciej Bzowski |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086371
|
| Publikation (Nr.) |
 EGU/EGU2014-223.pdf |
|
|
|
|
|
| Zusammenfassung |
| Full sky maps of energetic neutral hydrogen atoms (H ENA) obtained with the Interstellar
Boundary Explorer revealed a bright, arc-like Ribbon, which dominates over the heliosheath
emission on large swaths of the sky. We simulate the emission of helium ENA from the
heliosheath and the IBEX Ribbon. To estimate the heliosheath signal, we use a set of simple
models of the heliosphere, where we take the newest results from the Voyagers spacecraft
into account. We simulate the evolution of energy spectra of α-particles and He+ ions using a
number of binary interactions of He ions with plasma and neutral background in the
heliosheath. The suprathermal ions from this distribution are a source of emerging He ENA
flux, which we calculate. The fluxes in the observer frame are corrected for the
Compton-Getting effect and the re-ionization losses on the path to detector. We conclude
that the highest intensities should be expected from the heliospheric tail. For 1
keV He ENA, they are ~ 0.5 - 10 (cm2 ssrkeV )-1, depending on the employed
model, whereas the expected intensities in the forward and flank sectors of the
heliosphere in models with the heliosheath thickness ~ 25 AU do not exceed 0.02
(cm2 ssrkeV )-1 and 0.2 (cm2 ssrkeV )-1, respectively. For assessment of the
IBEX Ribbon emission we compare the He ENA emissions from two models of
the Ribbon origin previously developed to explain the hydrogen emission. In the
first one, the Ribbon ENAs are produced outside the heliopause from the ionized
neutral solar wind in the direction where the local interstellar magnetic field is
perpendicular to the line-of-sight. The second model proposes the ENA production at the
interface between the Local Interstellar Cloud (LIC) and the Local Bubble (LB). In
the first model, the expected intensity is ~ 0.014 (cm2 ssrkeV )-1, i.e., of the
order of the emission from the forward sector of the heliosphere, whereas in the
second model, the intensity is ~ 2 - 7 (cm2 ssrkeV )-1. If the IBEX Ribbon
requires a source population of ENAs leaving the heliosphere, then the Ribbon
should not be visible in He ENA because of the insufficient supply of the He ENA
from the neutralized α-particles from the solar wind. Full-sky measurements of
He ENA could create a possibility of distinction between proposed models of the
Ribbon origin. We check that He ENA have a potential to probe distant sources
of ENA production owing to the expected long mean free path against ionization
and elastic scattering (up to 8000 AU for 1 keV/n He) in the interstellar medium. |
|
|
|
|
|
|