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Astron. Astrophys. 341, 296-303 (1999)

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8. Discussion

Comparing the mass distribution of detected particles to model calculations of [FORMULA]-values as a function of size, we expect the [FORMULA]-meteoroids to have [FORMULA]-values which are larger or equal 0.2. The observed flux rate is then best described with a wide distribution of perihelion distances and the present analysis shows no preference for small perihelion distances. The flux rate of particles that are produced within about 0.1 AU (about 20 solar radii) around the Sun would drop down already in the region beyond 2 AU. This indicates that [FORMULA]-meteoroids identified in the Ulysses data set originate primarily from collisions, because the origin of [FORMULA]-meteoroids by sublimation takes places inside 20 solar radii around the Sun (Mann et al., 1994). As compared to an early analysis by Whipple (1975) we do not assume a certain parent body to be the source of the [FORMULA]-meteoroids, but allow for a variety of initial orbits. Furthermore, the orbital parameters that Whipple used in his analysis are included in the present model assumptions.

Except for the dominance of particles that may be associated with prograde motion we do not see a clear indication for a preference for certain orbital inclinations. The fact that the particles have been detected at high ecliptic latitudes raises the question of whether the particles have been severely influenced by the Lorentz force in their dynamics. The effect of the Lorentz force on small electrically charged dust grains would lead to the ejection of particles from the near solar regions on a wire-like trajectory (Hamilton et al., 1996; Krivov et al., 1998). These models, however, do not allow for a direct comparison, so far, since they do not yield a detailed description of the orbital parameters of the expected fluxes. Hence at this point, we cannot give a clear description of the formation mechanism of the particles. The present result does not show a clear indication for a strong influence of electromagnetic forces: The derived distribution of the perihelion distances does not show a clear peak for very small perihelion distances and the detected [FORMULA]-meteoroids seem to show a majority of particles in prograde motion. The particles detected within the ecliptic have masses which are only slightly smaller than the [FORMULA]-meteoroids identified in the out of ecliptic part, so there is no clear indication that the out-of-ecliptic fluxes are produced by a different effect than the near-ecliptic fluxes.

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© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998