DETERMINATION OF THE ABUNDANCES OF SUBCORONAL 4He AND OF SOLAR FLARE-ACCELERATED 3He AND 4He FROM GAMMA-RAY SPECTROSCOPY

摘要

A series of narrow gamma-ray lines at 0.339, 0.429, 0.478, 0.937, 1.00, 1.04, 1.05, and 1.08 result almost exclusively from the bombardment of ambient He, O, and Fe by accelerated alpha-particles and 3He nuclei. Study of these lines, combined with the s6Fe line at 0.847 MeV and the 16O line at 6.129 MeV, allows the determination of the abundances of alpha-particles and sHe accelerated in solar flares and of the ambient He in the gamma-ray production region in the solar atmosphere. Using the Solar Maximum Mission/ GRS and Compton Gamma Ray Observatory/OSSE data for 20 flares, we find that with significance not exceeding about 2.5 delta there are flares that exhibit alpha-particle abundance enhancements (alpha/p > 0,1), show evidence for the presence of accelerated 3He, and indicate ambient He abundance enhancements. In some cases the accelerated `3e/4He ~ 1 , and for essentially all of the flares 3He/4He could be 0.1, con- sistent with our earlier conclusion that in both impulsive and gradual flares the particles that interact and produce gamma rays are always accelerated by the same mechanism that operates in impulsive flares, namely, stochastic acceleration through gyroresonant wave-particle interactions, The ambient He abundance enhancements suggest that there are chromospheric regions where He/O exceeds its photo- spheric value, a result that could have important implications for solar atmospheric dynamics.