Other
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsh24a..01b&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #SH24A-01
Other
2114 Energetic Particles (7514), 2124 Heliopause And Solar Wind Termination, 2126 Heliosphere/Interstellar Medium Interactions, 2151 Neutral Particles (7837), 2152 Pickup Ions
Scientific paper
Here we report on the first three years of spectral observations across the sky of ENAs in the ˜0.3-3 keV range generated in the heliosheath observed by NPD on board Venus Express. The observed spectral shapes are consistent with the expected ENA spectra derived from the Voyager-1 and 2 observations, but with an additional "ledge" starting at around 0.5 keV extending to a drop at a couple 1.0 keV. We interpret this additional feature as the enhancement of ions picked-up by the solar wind and convected out into the heliosheath. Furthermore, plasma and energetic particle measurements during the termination shock crossings by the Voyagers reveal that most of the solar wind flow energy is tranferred into the particles in the pick-up ion energy range (˜0.1-10 keV) [Richardson, Nature, July, 2008] - a range that was not covered by the Voyager instrumentation, but is covered by the ASPERA-4/NPD measurements. We seek to estimate if the observed ENA spectra are consistent with the required energization at these energies. To date the statistical coverage of the NPD observations are sufficient to obtain statistically significant spectra in 60x60 deg angular bins (higher resolution close to the ecliptic equator), covering all ecliptic longitudes and up to about 60 deg northern and southern ecliptic latitudes. High-resolution measurements of the entire sky are soon expected from the Interstellar Boundary Explorer (IBEX), which is the only mission so far dedicated to imaging the heliosheath and was launched October 2008. While the IBEX data is currently being analyzed, several other, non-dedicated instruments on board various missions (Venus Express, Cassini, IMAGE, Mars Express, SOHO, STEREO) are seeking to provide meaningful measurements of the structure and spectral characteristics of the heliosheath. These continuing efforts will be particularly important to study the possible temporal variations of the heliosheath ENA signals, which would be a important constraint on the spatial extent and dynamics of the heliosheath. NPD belongs to the ASPERA-4 experiment suite on board VEX and is a time-of-flight (TOF) instrument using a coincidence technique to identify ENAs (and is therefore not sensitive to, for example X-rays) and has an instantaneous field-of-view (FOV) of 5°×180° with six sectors of each 5°×30° FOV. A scanning platform allows the FOV to scan across half of the entire sky in one scan.
Barabash Sergey V.
Bazell David
C:son Brandt Pontus
Decker Roger
DeMajistre Robert
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