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L. Strachan, R. Suleiman, A. V. Panasyuk (Harvard-Smithsonian Center for Astrophysics), D. A. Biesecker (NASA/GSFC and Emergent IT), J. L. Kohl (Harvard-Smithsonian Center for Astrophysics)
We use combined Ultraviolet Coronagraph Spectrometer (UVCS) and Large Angle Spectroscopic Coronagraph (LASCO) data to determine the O(5+) outflow velocities as a function of height along the axis of an equatorial streamer at solar minimum and as a function of latitude (at 2.3 solar radii from sun center). The results show that outflow increases rather abruptly in the region between 3.6 and 4.1 solar radii near the streamer cusp, and gradually increases to ~90 km/s at about 5 solar radii in the streamer stalk beyond the cusp. The latitudinal variation at 2.3 solar radii shows that there is no outflow (within the measurement uncertainties) in the center of the streamer called the core, and that a steep increase in outflow occurs just beyond the streamer legs, where the O VI 1032 intensity relative to H I 1216 (Ly alpha) is higer than in the core. Velocity variations in both height and latitude show that the transitions from no measurable outflow to positive outflow are relatively sharp and thus can be used to infer the location of the transition from closed to open field lines in streamer magnetic field topologies. Such information, including the densities and kinetic temperatures derived from the observations, provides hard constraints for realistic theoretical models of streamers and the source regions of the slow solar wind.
This work is supported by NASA Grant NAG5-11420 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by the ESA PRODEX program (Swiss contribution). do not accept author defined LaTeX macros.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.