Accelerated and Ambient He Abundances from Gamma-Ray Line Measurements of Flares

Details Accelerated and Ambient He Abundances from Gamma-Ray Line Measurements of Flares Accelerated and Ambient He Abundances from Gamma-Ray Line Measurements of Flares

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...508..876s&link_type=abstract

The Astrophysical Journal, Volume 508, Issue 2, pp. 876-884.

Astronomy and Astrophysics

Astronomy

37

Sun: Solar Wind, Sun: Abundances, Sun: Flares, Sun: Photosphere, Sun: X-Rays, Gamma Rays

Scientific paper

The gamma-ray lines from ^7Be and ^7Li produced when flare-accelerated He nuclei interact with ambient He have been found to be surprisingly intense from measurements made by moderate-resolution gamma-ray spectrometers on the Solar Maximum Mission (SMM) and Compton Gamma Ray Observatory (CGRO) satellites. These high intensities suggest either accelerated alpha/proton ratios >~0.5 and/or an He/H abundance greater than 0.1 in the subcoronal regions where the particles interact. We have studied additional gamma-ray lines in 20 flares produced by interactions of alpha particles on ^56Fe and other elements to resolve this ambiguity. These measurements indicate, on average, that the ambient He abundance is consistent with accepted photospheric values and that an enhanced concentration of He is present in flare-accelerated particles. Although there is evidence for the presence of accelerated ^3He, its concentration is only a fraction of accelerated ^4He. These studies also revealed a new weak line in the spectra at ~1.32 MeV that is attributed to an excited state of ^55Fe.

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