O5+ in High Speed Solar Wind Streams: SWICS/Ulysses Results |
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Authors: | Robert F Wimmer-Schweingruber Rudolf Von Steiger Johannes Geiss George Gloeckler Fred M Ipavich Berend Wilken |
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Institution: | 1. Physikalisches Institut, Universit?t, Bern, Switzerland 2. International Space Science Institute, Bern, Switzerland 3. Dept. of Physics, University of Maryland, Maryland, USA 4. Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany
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Abstract: | Recent observations with UVCS on SOHO of high outflow velocities of O5+ at low coronal heights have spurred much discussion about the dynamics of solar wind acceleration. On the other hand, O6+ is the most abundant oxygen charge state in the solar wind, but is not observed by UVCS or by SUMER because this helium-like
ion has no emission lines falling in the wave lengths observable by these instruments. Therefore, there is considerable interest
in observing O5+ in situ in order to understand the relative importance of O5+ with respect to the much more abundant O6+. High speed streams are the prime candidates for the search for O5+ because all elements exhibit lower freezing-in temperatures in high speed streams than in the slow solar wind. The Ulysses
spacecraft was exposed to long time periods of high speed streams during its passage over the polar regions of the Sun. The
Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is capable of resolving this rare oxygen charge state. We present
the first measurement of O5+ in the solar wind and compare these data with those of the more abundant oxygen species O6+ and O7+. We find that our observations of the oxygen charge states can be fitted with a single coronal electron temperature in the
range of 1.0 to 1.2 MK assuming collisional ionization/recombination equilibrium with an ambient Maxwellian electron gas.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | Solar wind solar wind acceleration corona |
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