Results of observations of the dust distribution in the F-corona of the sun

Abstract

The results of modeling of the distribution of dust in the circumsolar zone are presented. The dust distribution was retrieved from observations of the line-of-sight velocities in the F-corona to the distances of 7–11 solar radii during the total eclipses of the Sun in different years: on July 31, 1981; August 11, 1991; March 29, 2006; and August 1, 2008. Comparison of the results has shown that the dust composition varies from year to year and the dust is dynamically nonuniform. In addition to the dust related to the zodiacal cloud and concentrating to the ecliptic plane, the dust of retrograde motion and the ejections and accretion in the polar regions are observed. From the results of observations of eclipses on July 31, 1981, August 11, 1991, and August 1, 2008, the east–west asymmetry in a sign of the line-of-sight velocities was detected: they are negative to the east of the Sun and positive to the west. Such distribution of the velocities is indicative of the nearecliptic orbital dust motion, whose direction coincides with that of the motion of the planets. In the course of the eclipse of March 29, 2006, almost no dynamical connection with the zodiacal cloud was found. At the same time, the direction, where the observed velocities are largest in value and opposite in sign on opposite sides of the Sun, was determined, which provides evidence of the orbital motion deviating from the ecliptic plane. The results of observations in 2006 reveal a clear genetic connection of the observed orbital motion of dust with the parent comets of the Kreutz family found near the Sun close to the eclipse date. The velocities observed near the symmetry line in the plane of the sky grow by absolute value with increasing the elongation, which may take place, if the line of sight croßses an empty zone that is free of dust. The modeling of the data of observations near the symmetry plane allowed the parameters of the dust distribution near the sublimation zone to be obtained. In 2006, the “black” cometary dust with a low albedo (A = 0.05) was observed; it showed high values of the power-law exponents in the distance distribution of the dust concentration (V = 2.2 > 1) and in the size distribution of grains (γ = 5.2 > 4.0) and a strong radiation pressure (β = 0.70–0.74). We estimated the mean radius of grains as ≈0.8–0.9 µm and the radius of the dust-free zone as ≈9.1–9.2 solar radii. The latter corresponds to the distances, where the low-melt components of olivines and pyroxenes disintegrate. In 2008, the observed zodiacal dust concentrating to the ecliptic plane demonstrated the canonical parameters: A = 0.1–0.2, V ≈ 1, ß ≈ 0, γ = 4.0, the mean radii of grains were 0.9–1.2 µm, and the radius of the dust-free zone was 7.0–7.6 solar radii.