Lay, G. | Search NASA

NASA NTRS1984

IUE high resolution spectrophotometry of H Ly alpha emission from the local interstellar medium

IUE high dispersion spectra of resonantly scattered solar Ly alpha emission from H moving into the solar system with the local interstellar wind are reported which are based on observations conducted in April 1981 and April 1983. A heliocentric velocity of -29 + or - 5 km/s has been observed from the ISW component along with a surface brightness which has decreased from about 1000 to 800 Rayleighs over the two-year interval. A preliminary derivation of the velocity of the ISM at large distances from the sun yields a value of 25.6 + or - 5 km/s.

Clarke, J. T.↗

NASA NTRS1981

A search for interplanetary He II, 304-A emission

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.

Paresce, F.↗