A study on solar dust ring formation based on fractal dust models

Using the fractal aggregate model for circumsolar dust grains, the nature of the circumsolar dust clouds is examined. As a fractal dimension of the aggregate decreases, the porosity of the aggregate increases. Consequently, its temperature becomes independent of its size, and approaches that of its constituent particles. This evidence suggests that the fractal aggregates with different sizes and made of the same chemical components sublimate at the same solar distance. This implies that the distance of the sublimation zone depends on the chemical composition alone. We have found that the aggregates consisting of silicate material, as well as carbon material, sublimate in the solar F-corona.On the other hand, a ratio of radiation pressure force to solar gravity on the fractal aggregate scarcely increases with decreasing size due to sublimation, in contrast with a strong dependence of its ratio on its size for a compact sphere. Our computer simulation for dynamical evolution of fractal aggregates suggests that they produce a narrow ring structure in the circumsolar dust cloud, compared with that expected for spherical dust grains. When the aggregates have more fluffy structure with a small fractal dimension, however, it is found that the circumsolar dust clouds would make no remarkable ring structure.