Visible Helium Spectrum of a White-Light Flare

摘要

Emission lines of neutral and ionized helium at visible wavelengths are measured in the white-light flare of 24 April 1981. These intensities, along with accompanying profiles, are presented for the purpose of providing an observational basis for future radiative transfer models of white-light flares. Absolute intensities, both peak and integrated, are given for 14 lines of Helium I, and for the He II line at 4686. We compare intensities of these lines in the white-light emitting region to intensities measured in a flare kernel that does not show significant continuum emission. From this, we infer that the white light emission arises from material at chromospheric temperatures, and not from temperatures greater than about 20,000 K. A search for Stark-enhanced forbidden neighbors to the allowed He I lines in this disk flare was unsuccessful. From measurements of the He I 4026 line profile in the non-white-light emitting kernel of this flare, we set an extreme upper limit on the electric field in the He I emitting region of 1400 V per cm.