Abstract:
We derive from SOHO/CELIAS/CTOF data a value for the elemental Fe/O ratio in the solar wind. Since Fe is a low FIP element and O a high FIP element their relative abundance is diagnostic for the FIP fractionation process. Though our absolute value of Fe/O still may slightly change pending the recalibration of the sensor, the overall dependence on the solar wind speed is not affected by these uncertainties. The Fe density is calculated from the charge states 7+ to 16+ and the O density from the charge states 6+ and 7+ which covers 95\% or more of the total density of both species.
The unprecedented time resolution of the sensor allows a fine scaled study of the Fe/O ratio as a function of the solar wind bulk speed. The speed ranged between 300 km/s and less than 600 km/s in the period of observation. The Fe/O abundance shows a continuos decrease with increasing solar wind speed by a factor of two between 350 km/s and 500 km/s. This corresponds to the well-known FIP effect dependence. Our value at about 500 km/s commensurates well with the previously observed Fe/O abundance in polar coronal holes. The implications of our results on the FIP fractionation models are discussed.