Other
Scientific paper
Nov 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984nascp2345...24s&link_type=abstract
In NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81 p 24-27 (SEE N85-15539 06-90)
Other
16
Abundance, Helium, Hydrogen, Interstellar Space, Lyman Alpha Radiation, Pioneer 10 Space Probe, Voyager 2 Spacecraft, Optical Thickness, Photometry, Solar Flux, Solar Mesosphere Explorer, Spectroscopy, Time Dependence
Scientific paper
The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 A was applied to a determination of atomic hydrogen and helium densities. These density estimates obtained from direct measurement of scattered radiation depend on absolute calibration of the instruments in the same way as other earlier determinations based on the same method. However, the spacecraft data were combined with daily ll sun averages of the H Lyman 1216 A line obtained by the Solar Mesospheric Explorer satellite to obtain a measure of atomic hydrogen density independent of instrument absolute calibration. The method depends on observations of long and short term temporal variability of the solar line over a one year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are H = 0.12/cu cm and H = .016/cu cm, giving a density ratio close to the cosmic abundance value in contrast to some earlier results indicating a depletion of atomic hydrogen. Estimates were obtained of galactic background emissions in the signals of both spacecraft.
Jessen J. M.
Judge Darrell L.
Shemansky Don E.
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