Lyman continuum observations of solar flares

A study is made of Lyman continuum observations of solar flares, using data obtained by the Harvard College Observatory EUV spectroheliometer on the Apollo Telescope Mount. It is found there are two main types of flare regions: an overall 'mean' flare coincident with the Hα flare region, and transient Lyman continuum kernels which can be identified with the Hα and X-ray kernels observed by other authors. It is found that the ground level hydrogen population in flares is closer to LTE than in the quiet Sun and active regions, and that the level of Lyman continuum formation is lowered in the atmosphere from a mass column density m approximately 10-3 g cm-2 in kernels. From these results the amount of chromospheric material 'evaporated' into the high temperature region is derived which is found to be approximately 1015 g, in agreement with observations of X-ray emission measures. A comparison is made between kernel observations and the theoretical predictions made by model heating calculations, available in the literature; significant discrepancies are found between observation and current particle-heating models. (Auth.)