Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aps..dmp..k104k&link_type=abstract
American Physical Society, DAMOP Meeting, 27-30 May 1998 Santa Fe, New Mexico, abstract #K1.04
Astronomy and Astrophysics
Astrophysics
Scientific paper
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) is designed to obtain an empirical description of the extended solar corona and its expansion into the solar wind. During its first two years of operation, UVCS has been used to determine velocity distributions and bulk motions of protons, electrons and minor ions; particle densities, and elemental abundances from near the base of the solar corona to heliocentric heights up to 10 solar radii. Measurements of spectral line profiles and comparisons of observed intensities with self consistent coronal models are used to derive values for the coronal plasma parameters. The measurements are challenging the current theories on the composition and acceleration of the solar wind. The velocity distributions for coronal ions are found to be anisotropic by as much as a factor of 15 and the most probable speeds in the direction perpendicular to the coronal magnetic field are extremely large reaching values corresponding to temperatures of over 2 × 10^8 K in a thermalized plasma. Elemental abundances in specific coronal structures can be an order of magnitude smaller than in the solar photosphere. Similarities between abundances in the corona and abundances in fast and slow wind streams provide clues about the coronal source regions of the wind. The physical processes and atomic parameters required to derive the coronal parameters from the observations will be discussed. Current ideas about the theoretical explanation for the derived empirical description of the corona will also be described briefly. This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana and by Swiss funding agencies.
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