FRACTAL AGGREGATE ANALOGS FOR NEAR SOLAR DUST PROPERTIES

The present study compares properties of near solar dust, deduced from inversion of F-corona brightness data, with calculations of fluffy ag gregate particles. It is shown that silicate particles containing a sl ight amount of absorbing material have temperatures below the blackbod y temperature if the impurity amounts to less than 0.1% in volume. Thi s effect is especially significant for porous particles and points to the existence of such a component, possibly cometary dust, in the sola r vicinity. In particular the silicate particles with a large impurity , which show a higher temperature than the blackbody at the same solar distance, sublimate at a larger solar distance. As the impurity decre ases, the sublimation starts closer to the sun and the pure silicate, if it would exist, would survive even at about 2 solar radii from the sun. This result which is based on calculations that apply model mater ials, may possibly explain the wide extended zone of sublimation deriv ed from F-corona brightness data. Another finding of our calculations is an unexpected enhancement of temperature of the two-component aggre gates. Namely the silicate aggregate with absorbing impurities attains higher temperature even than the pure carbon. This happens when the v olume fraction of absorbing material exceeds 1% and the aggregate with a fractal dimension of 2.98 is located below about 100 solar radii fr om the sun; this critical solar distance depends on the volume fractio n of absorbing material. A similar trend was also seen in the compact particle consisting of two components. This comes from the complex dep endence of the energy loss from the particle on the temperature.