On the Enhancement of Certain Helium Lines in the Limb Flare of June 24,1956.

Abstract

An unusually well-observed limb flare occurred on June 24,1956. The lines 4471, 4713, 4922, and 6678 of neutral helium, 4686 of ionized helium, and Ha and H appear strongly in the spectra. The intensities of 4471, 4686, 4713, and 4922 are about equal. The temperature of the flare is deduced by comparing the Doppler half-widths of the helium and hydrogen lines and, more accurately, from the relative intensities of 4686 and 4471. Both methods give roughly 30000 . The anomalous excitation of 4713 and 4922 are studied in terms of the helium equilibrium. It is found that at high temperature and densities these lines, as well as certain other helium lines, are strongly excited relative to 4471 and 5876 by collisions from the liS ground state of helium. The conditions necessary are T > 30000 and N > 3 X 1012.