Velocity of iron ions in the solar wind

From a set of approximately 7000 spectra provided by the ISEE 3 ion composition instrument at the time near the maximum of solar cycle 21 we have been able to derive iron velocities and to compare them with velocities of helium ions obtained with the same instrument. We find a strong correlation among these velocities (r_cor =0.975+/-0.001). Whereas no significant velocity differences between helium and iron are found at low solar wind speeds, it appears that iron tends to flow at a somewhat lower speed (Δv~10 km/s) in high-speed streams.