On intensity ratios of helium and hydrogen lines in quiescent prominences

Abstract

Observations of the lines He i λ 3888 and H8 in 80 quiescent prominences by the author, and in other prominences by Kubota et al. (1972) and Morozhenko (1971), have been used to derive the dependences of I(3888)/I(H8) on I(H8), N23s on τ0 (H), and N+ne on τ0(H) (Figures 1, 2, 3 and 4). The equations of ionization equilibrium and triplet system steady state for a helium atom (27 levels and continuum were considered) were solved together with the radiation transfer equation in the helium Lyman continuum. As given ne(τ) distribution with depth and Te=7500 K were assumed. The 23S level population N23s, helium emission measure N+ne and the intensity ratios of the He i λ 3888 and H8 lines were calculated and compared with observation (Figures 2, 3 and 4, solid lines). The figures show that in bright prominences the observed values of N23s and N+ne are systematically higher than the calculated ones. These deviations cannot be eliminated by decreasing ne. One can make the calculations and observations agree for bright prominences by increasing the UV radiation which penetrates into the prominence.