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Uranian H Ly‐α emission: The interstellar wind source
Author(s) -
Yelle R. V.,
Sandel B. R.
Publication year - 1986
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl013i002p00089
Subject(s) - physics , astrophysics , scattering , brightness , solar wind , interstellar medium , astronomy , hydrogen , galaxy , plasma , optics , quantum mechanics
IUE observation of Uranian emissions in hydrogen Lyman alpha (H Ly‐α over, the past four years have recently been summarized by Clarke et al. [1985]. Over this time period they find an average H Ly‐α brightness of 1260 R which they estimate is composed of 200 R of solar scattered radiation and 1060 R from a collisional source. A third component, not considered by previous authors, is the reflection of H Ly‐α emissions from the interstellar wind. Hydrogen in the interstellar wind forms an extended source of H Ly‐α whose importance relative to the solar flux increases with distance from the sun. We demonstrate that scattering of interstellar H Ly‐α is more important than scattering of solar H Ly‐α for reasonable values of H column abundance and, in fact, may make up 10 ‐ 40% of the observed signal. Large H column abundances are still required to explain the H Ly‐α brightness solely on the basis of resonant scattering; therefore it is likely that the emissions are due in part to collisional sources and in part to the scattering of interstellar H Ly‐α with solar scattering playing a minor role.