Temperature Anisotropies of heavy solar wind ions from Ulysses-SWICS

We report the first in-situ measurements of temperature anisotropies of heavy ions in the solar wind, obtained with the Solar Wind Ion Composition Spectrometer (SWICS) on the Ulysses spacecraft. Since SWICS measures only 1-dimensional cuts through the full, 3-d velocity distribution functions we resort to a statistical approach, separating the particle data according to the instantaneous magnetic field angle. We apply this analysis to the ions of He++ and O6+ during extended time periods in the fast streams from both the south and the north polar coronal holes that Ulysses traversed in 1993-96. In both cases we find anisotropies of the order of T-perpendicular to/T-parallel to = 0.8. The results of this study are discussed in relation to the observations made on Helios for He++ in the 1970s, and to recent observations made on SOHO-UVCS, which show extreme temperature anisotropies of O VI, or O5+, at a few solar radii.