Abstract
The results of the following investigations on dust and gas in the F corona are reviewed: firstly, interferometric observations of the radial velocities of dust using the Doppler shifts of Frauhofer lines obtained during two total solar eclipses on July 31, 1981 and July 11, 1991; secondly, modelling of the orbital evolution of dust grains near the Sun during their evaporation; thirdly, prediction of the resonance emission of gas formed near the Sun after evaporation of dust, solids and comets, together with the search for and discovery of emission in K line of Ca I, analysis of the Ca-ion acceleration mechanism, and a model of the expanding envelope; fourthly, the mechanism of thermal disintegration of both icy and non-icy bodies approaching the Sun in highly eccentric orbits, which was considered to be the source of dust grains and gas particles in the circumsolar region. Analytical and numerical solutions of the heat diffusion equation were used. Thermal stresses which arise inside and at the surface of solids can exceed by several orders of magnitude the tidal stresses in the neighbourhood of the Sun and play an important and possibly crucial role in the evolution of comet-like bodies.