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Doppler Dimming Determination of Coronal Outflow Velocities

 

Measurements of outflow velocities of coronal hydrogen and other ions, in conjunction with measurements of particle densities and temperatures, are useful for determining mass and energy fluxes as a function of distance in the corona. Velocity data in the region 1.2 to 10 R are lacking in comparison to the abundance of data beyond 0.3 AU. The regions of the corona inside 10 RSUN are particularly interesting because they are believed to be the regions where significant acceleration of coronal material takes place. Also, by determining the outflow velocities of different coronal constituents, specifically protons (or neutral hydrogen) and O, it may be possible to distinguish differences in outflow velocities among different particles and as a function of height. These results should lead to a better understanding about the acceleration of minor ion species into the solar wind.

With UVCS we hope to make use of the Doppler dimming method (Withbroe et al. 1982) to determine outflow velocities of neutral hydrogen and O in various coronal structures. The velocities perpendicular to the line-of-sight are determined by measuring the resonantly scattered intensities of H I and O VI . For H I , the velocity determination depends on measurements of the H I disk intensity and electron density measurements inferred from white light observations. Similar quantities are needed for the determination of O velocities; however, the ratio of the O VI doublet line intensities will add additional constraints on what values the outflow velocities can have. Similar measurements can be made for Mg X and Si XII.

Doppler Dimming Determination of Coronal Outflow Velocities



Peter Smith
Fri Jan 17 12:11:15 EST 1997