Measurements of Solar Wind Sulfur Abundance and Charge States.

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Using the Solar Wind Ion Composition Spectrometer on Ulysses, the abundance of sulfur relative to silicon and oxygen has been determined for three types of solar wind: coronal hole flows, quiet time periods and driver plasma streams. Values of S/Si = 0.37 +/- 0.09, S/O = 0.050 +/- 0.009; S/Si = 0.29 +/- 0.09, S/O = 0.053 +/- 0.013; S/Si = 0.33 +/- 0.10, S/O = 0.0776 +/- 0.007 were determined for coronal hole, quiet time and driver plasma flows respectively. The abundances suggest a reduction of the first ionization potential (FIP) effect in coronal holes. The individual logarithmic abundances of S, Si and O (log H = 12) for the coronal hole, quiet time and driver plasma flows were S = 7.04 +/- 0.11, Si = 7.52 +/- 0.14, O = 8.41 +/- 0.12; S = 6.87 +/- 0.22, Si = 7.46 +/- 0.11, O = 8.21 +/- 0.14; S = 6.91 +/- 0.42, Si = 7.43 +/- 0.30, O = 8.10 +/- 0.21. These values suggest high FIP elements are depleted in the corona. The relative abundance of sulfur charge states were also measured. Sulfur ion fractions are consistent with equilibrium models for coronal hole and quiet time flows but not for driver plasma flows. Each flows type exhibited an overabundance of low charge states relative to the model predictions. Ionization temperatures from adjacent charge state abundance ratios yielded average values for S, Si and O of 1.5 +/- 0.1, 1.3 +/- 0.1, 1.2 +/- 0.2 (coronal hole), 1.6 +/- 0.2, 1.4 +/- 0.1, 1.5 +/- 0.2 (quiet time), 2.0 +/- 0.3, 1.7 +/- 0.2, 2.1 +/- 0.2 (driver plasma). Higher temperatures in driver plasma flows and lower values in coronal hole flows are consistent with previous determinations for silicon and iron. These coronal holes ionization temperatures with other reported results indicate that sulfur freezes-in near the temperature maximum. Our sulfur results represent the first in situ determinations of sulfur abundance and charge states in the solar wind.

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