The Fe/O elemental abundance ratio in the solar wind as observed with SOHOCELIAS CTOF

Using data of the Charge Time-of-Flight (CTOF) mass spectrometer of the Cha rge, Element, and Isotope Analysis System (CELIAS) on board the Solar and H eliospheric Observatory (SOHO) from similar to 80 days of observation aroun d solar minimum we derive a value for the Fe/O abundance ratio for the inec liptic solar wind of 0.11 +/- 0.03. Since Fe has a low first ionization-pot ential (FIP) and O is a high-FIP element, their relative abundance is diagn ostic for the FIP fractionation process. The unprecedented time resolution of the CELIAS CTOF sensor allows a fine-scaled study of the Fe/O ratio as a function of the solar wind bulk speed. On average, the Fe/O abundance rati o shows a continuous decrease by a factor of 2 with increasing solar wind s peed between 350 and 500 km/s. This corresponds to the well-known FIP effec t dependence. Our value at similar to 500 km/s agrees with the previously o bserved Fe/O ratio in the fast solar wind emerging from polar coronal. hole s whereas the value for speeds below 350 km/s is consistent with a remote a bundance determination in the leg of a coronal streamer. The variability of the Fe/O abundance ratio is much larger in the slow than in the fast solar wind.