The Si/O Abundance Ratio in the Solar Wind Measured With CELIAS/CTOF and the Search for the FIP Effect in Coronal Hole Associated Wind

Authors: M.R. Aellig, H. Holweger, S. Hefti, P. Wurz, H. Grünwaldt, F.M. Ipavich, and P. Bochsler.

Submitted an abstract to the AGU fall meeting 1998.

Because of the 3-axis stabilization of the spacecraft and thanks to the 100% duty cycle the sensor provides data with very good counting statistics and high time resolution.

A major uncertainty in determining the efficiency of the FIP fractionation process arises from the uncertainties of the photospheric abundances of Si and O. To further reduce these uncertainties we make an attempt to determine the photospheric Si/O directly from observations. Instead of relating independently determined Si and O values from photospheric abundance tables, we minimize the experimental uncertainties by reducing the influence of parameters which arise from uncertainties of photospheric models with a careful selection of the lines.

To identify the source region of the solar wind, we use optical observations, the solar wind speed, the in situ determined oxygen freeze-in temperature, and the preliminary He/H solar wind abundance derived from SOHO/CELIAS/MTOF. We discuss our results in the context of other recent experimental data and compare it with predictions of theoretical models on the FIP effect in coronal hole associated solar wind.

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Last Update: Septmeber 8, 1998, James Weygand