Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981jgr....8610038p&link_type=abstract
Journal of Geophysical Research, vol. 86, Nov. 1, 1981, p. 10038-10048.
Astronomy and Astrophysics
Astronomy
7
Emission Spectra, Helium Ions, Interplanetary Gas, Ultraviolet Astronomy, Apollo Soyuz Test Project, Extreme Ultraviolet Radiation, Gas Spectroscopy, Line Spectra, Plasma Currents, Spaceborne Telescopes
Scientific paper
A survey of a region of the sky around the antisolar direction in the earth's shadow was surveyed by the extreme ultraviolet telescope on the Apollo-Soyuz mission, whose 170-620 A channel is primarily sensitive to the H II, 304-A and He I, 584-A resonance. A sharp decrease in intensity was found as the line of sight sweeps into the shadow region. Once the line of sight is contained within the shadow, a residual signal above instrumental background was observed that was independent of view direction and spacecraft position. An upper limit at the 2sigma confidence level to a possible He II, 304-A component that can escape detection by the instrument corresponds to 0.002 R, or to a column density of 10 to the 9th ions/sq cm scattering at line center. The brightest possible sources for such emissions are multiple scattering from plasmaspheric He(+) in the shadow and scattering from He(+) created by the photoionization of the interstellar wind neutral helium.
Fahr Hans
Lay Gary
Paresce Francesco
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