非表示:
キーワード:
dust, interstellar, Ulysses, heliosphere, solar maximum, dynamics.
要旨:
We analyze the Ulysses in situ measurements of interstellar dust in the solar system with respect to the temporal variation of the flux density. The data set that is used covers the time from after Ulysses' fly-by of Jupiter up to the most recent data taken end of November 2002. The decrease in interstellar dust flux observed in 1996 can be explained by the interaction of the small, electrostatically charged grains with the solar wind magnetic field during the solar minimum with the polarity prevailing since 1991, as was reported earlier. Now with the new data, taken especially between 2000 and the end of 2002, we find that the amplitude of the decrease and the timing of the rebound with the 2000/2001 solar maximum is such that grains with relatively high charge to mass ratio of 1.33 C kg-1 and effective radii of 0.2 µm cannot account for the observed profile, as was concluded earlier. The simulation of the interaction of charged dust grains with the solar wind magnetic field shows that the best fit to the observations is achieved when the interstellar dust stream is dominated by grains with a charge to mass ratio of 0.59 C kg-1 and a radiation pressure efficiency factor of β = 1.1, which corresponds to an effective radius of 0.3 µm. We predict that the cumulative interstellar dust flux measured by Ulysses will level off at a constant value greater than 1 × 10-4 m-2 s-1 until the end of 2004.
