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Pioneer 10 and Voyager Observations of the Interstellar Medium in Scattered Emission of the He 584 A and H Lyα 1216 A Lines

Published online by Cambridge University Press:  12 April 2016

D.E. Shemansky ,
D.L. Judge  and
J.M. Jessen
D.E. Shemansky
Affiliation:
Center for Space Sciences, University of Southern California
D.L. Judge
Affiliation:
Center for Space Sciences, University of Southern California
J.M. Jessen
Affiliation:
Center for Space Sciences, University of Southern California

Abstract

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The combination of Pioneer photometric and Voyager spectrometric observations of EUV interstellar-interplanetary emissions in the region beyond 5 AU have been 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, we have combined the spacecraft data with daily full sun averages of the H Lya 1216 A line obtained by the Solar Mesospheric Explorer (SME) 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 1 year period, and the fact that the ISM is optically thick. The density estimates from preliminary work on these observations are [H] = 0,12 cm-3 and [He] = .016 cm-3, giving a density ratio close to the cosmic abundance value, in contrast to some earlier results indicating a depletion of atomin hydrogen. We have obtained estimates of galactic background emissions in the signals of both spacecraft.

Type
Helium and Hydrogen Backscattering Results and the Very Local Interstellar Medium
Information
International Astronomical Union Colloquium , Volume 81: Local Interstellar Medium , 1984 , pp. 24 - 27
Copyright
Copyright © NASA 1984

References

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