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G.A. Doschek, U. Feldman (Naval Research Laboratory)
We determine physical properties, such as electron temperature and density, in the Sun's west limb equatorial streamer region from spectra recorded by the SUMER spectrometer on SOHO. The spectra were recorded on 1996 November 21-22 during a special roll maneuver in which the stigmatic SUMER slit was oriented in the east-west direction. Results are obtained as a function of height from close to the limb out to about 1.5 solar radii. We find that the streamer region is well-represented by an isothermal plasma at 1.3 x 106 K between 1.03 and 1.5 solar radii. The electron density falls from 1.8 x 108 cm-3 near the limb to about 1.6 x 107 cm-3 at 1.3 solar radii. For ions with similar atomic weights, we find that the typical quiet Sun FIP enhancement of about a factor of 4 does not vary with height above the limb. Perhaps of most interest, we find strong evidence for gravitational settling of Fe relative to the lighter elements such as Ne, Mg, and Si. This adds a complicating factor in determining physical parameters in the corona. The above results are discussed in detail in Feldman et al. 1999, ApJ, 518, June 10 issue. We also measure the full width at half maximum intensity of spectral line profiles for lines of several upper transition region and coronal ions formed in the streamer. If we adopt our measured electron temperature and assume that the electron and ion temperatures are equal, we obtain typical nonthermal speeds of about 33 km s-1 and in addition find that the speed does not increase with height between about 1.03 and 1.3 solar radii. The line profile results are discussed in detail in Doschek & Feldman 1999, ApJ, submitted. This work was funded by the 6.1 NRL/ONR Solar Magnetism and the Earth's Environment Research Option.
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