Temperature tomography of the soft X-ray corona: Measurements of electron densities, temperatures, and differential emission measure distributions above the limb

We analyze long-exposure and off-pointing Yohkoh/SXT data of the solar coro na observed on 1992 August 26. We develop a new (temperature) tomography me thod that is based on a forward-fitting method of a four-parameter model to the observed soft X-ray fluxes F-1(h) and F-2(h) of two SXT wave-length fi lters as a function of height h. The model is defined in terms of a differe ntial emission measure (DEM) distribution dEM(h, T)/dT, which includes also a temperature dependence of density scale heights lambda (n)(T) = q(lambda ) lambda (T) and allows us to quantify deviations (q(lambda)not equal1) fro m hydrostatic equilibrium This parametrization facilitates a proper line-of -sight integration and relates the widely used filter ratio temperature T-F R to the peak of the DEM distribution. A direct consequence of the multi-sc ale height atmosphere is that the filter ratio temperature T-FR(h) is predi cted to increase with height, even if all magnetic field lines are isotherm al. 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 which underscores the dynamic nature of coronal q(lambda)less than or similar to 2.3, streamers. Our density measurements in coronal holes are slightly lowe r than most of the white-light polarized brightness inversions and seem to come closer to the requirements of solar wind models. Our DEM model provide s also a physical framework for the semiempirical Baumbach-Allen formula an d quantifies the temperature ranges and degree of hydrostaticity of the K, L, and F coronae.