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Session 4 - SOHO Corona II.
Oral session, Friday, June 27
Ballroom A, Chair: Therese Kucera

[4.04] The Electron Density, Temperature, and Si/Ne Abundance Ratio in Polar Coronal Holes from SUMER

G. A. Doschek (NRL), J. M. Laming (Sachs Freeman Associates), H. P. Warren (NRL), P. Lemaire (Institut d'Astrophysique Spatiale), K. Wilhelm (Max-Planck-Institut for Aeronomie)

The Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory (SOHO) covers a wavelength range with spectral and spatial resolution and sensitivity not previously obtained by any other solar spectrometer experiment. Consequently, new plasma diagnostic techniques have been used and developed to measure plasma parameters such as electron density. In this paper we discuss the electron density as a function of height above the solar surface in the polar coronal holes as determined from line ratios of Si VIII and S X. The densities vary between about 3 x 10^6 cm^-3 and 10^8 cm^-3. We determine the emission measure at selected temperatures as a function of position above the polar limbs from lines of Mg VII, Mg VIII, Mg IX, and Mg X. The electron temperature is lower in the polar holes than in the quiet Sun. This result is also based on intensities of lines of Fe X, Fe XI, and Fe XII. We determine the Si/Ne abundance ratio (low/high first ionization potential elements) using lines of Ne VII, Ne VIII, Si VII, and Si VIII. The preliminary result is that the Si/Ne abundance ratio in interplume regions is close to photospheric. We also compare the coronal hole density and abundance results with similar results obtained for the quiet Sun in the east and west coronal streamers. We discuss our conclusions in light of results from previous missions.

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