Charge states of C and O from coronal holes: Non-Maxwellian distribution vs. unequal ion speeds
Abstract
The Solar Wind Ion Composition Spectrometer (SWICS) on board Ulysses has compiled an extensive collection of ion charge state measurements in high-speed-wind streams. These provide important diagnostic constraints for the acceleration region of the large south polar coronal hole in which these charge states were ``frozen-in.'' Initial analyses of these data have inferred that the coronal electron distribution may deviate modestly from a Maxwellian (1) or that the coronal outflow speeds of heavy ions may vary with the ion mass (2) Here we apply a simple freezing-in approximation to examine the robustness and uniqueness of these inferences. In particular, we emphasize that careful attention to the ionization states of both Oxygen and Carbon provides the best potential diagnostic for a non-Maxwellian distribution of coronal electrons, since the similarity in their overall rate coefficients suggests a similar freezing-in location, while differences in their (comparatively high) ionization potentials provide a differential sensitivity to a high-energy electron tail. We also note the possibility that the freezing-in of the ionization state of these elements may begin in the underlying transition region of their source coronal hole.
- Publication:
-
Solar Wind Nine
- Pub Date:
- June 1999
- DOI:
- 10.1063/1.58758
- Bibcode:
- 1999AIPC..471..263O
- Keywords:
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- 96.60.Vg;
- Particle emission solar wind