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Tomography of the Soft X-Ray Corona: Measurements of Electron Densities, Temperatures, and Differential Emission Measure Distributions above the Limb View all abstracts by submitter

Markus J Aschwanden   Submitted: 2000-05-04 16:02

We analyze long-exposure and off-pointing {sl Yohkoh/SXT} data of the solar corona observed on 1992 Aug 26. We develop a new tomographic method which is based on a forward-fitting method of a 4-parameter model to the observed soft X-ray fluxes F_1(h) and F_2(h) of two {sl SXT} wavelength filters as function of height h. The model is defined in terms of a {sl differential emission measure (DEM)} distribution dEM(h, T)/dT, which includes also a temperature dependence of density scale heights {lambda}_n(T) =qlambda {lambda}_T and allows to quantify deviations (qlambda eq 1) from hydrostatic equilibrium, i.e. {lambda}_n(T)={lambda}_T. This parametrization faciliates a proper line-of-sight integration and relates the widely-used filter-ratio temperature TFR to the peak of the DEM distribution. A direct consequence of the multi-scale-height atmosphere is that the filter ratio temperature TFR(h) is predicted to increase with height, even if all magnetic field lines are isothermal. Our model-fitting reveals that coronal holes and Quiet Sun regions are in perfect hydrostatic equilibrium, but that coronal streamers have a scale height that exceeds the hydrostatic scale height by a factor of up to qlambdalapprox 2.3, which underscores the dynamic nature of coronal streamers. Our density measurements in coronal holes are slightly lower than most of the white-light polarized brightness inversions, and seem to come closer to the requirements of solar wind models. Our DEM model provides also a physical framework for the semi-empirical {sl Baumbach-Allen formula}, and quantifies the temperature ranges and degree of hydrostaticity of the {sl K-, L-, } and {sl F-corona}.

Authors: Markus J. Aschwanden and Loren W. Acton
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Publication Status: ApJ 550, 475-492
Last Modified: 2001-04-09 07:52
Go to main E-Print page  THE SPECTROVIDEOMAGNETOGRAPH REVEALS THE TRUE STRENGTH OF WEAK SOLAR FIELDS
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