Helium Resonance Lines in the Flare of 15 June, 1973

摘要

Time sequence of He l and He ll resonance line intensities at several siteswithin the flare of 15 June, 1973 are derived from observations obtained with the Naval Research Laboratory's Slitless Spectroheliograph on Skylab. The data are compared with predictions in six model flare atmospheres based on two values for the heating rate and three for the flux of photoionizing coronal X-rays and EUV. A peak ionizing flux more than 1000 times that in the quiet Sun is indicated. For most conditions in flare kernels the He ll L alpha and L beta lines are found to be formed by collisional excitation, thereby contributing to the local cooling of the plasma at temperatures above 60000 K. Emission in the higher Lyman lines is generally the result of a mixture of collisional excitation at these temperatures and photoionization and recombination at temperatures near 25000 K. We discuss implications for the common practice of deriving stellar coronal fluxes from He ll 1640 A fluxes assuming dominance of the recombination mechanism. Reprints. (JHD)