YOHKOH SOFT-X-RAY DETERMINATION OF PLASMA PARAMETERS IN A POLAR CORONAL HOLE

The Yohkoh Soft X-Ray Telescope (SXT) has been used to study the emiss ion from a coronal hole surrounding the north pole of the Sun. Stronge r emission from closed coronal structures in the line of sight can int erfere with attempts to measure properties of coronal hole plasma. SXT observations indicate that the north polar region was free of such co ntamination on 1992 October 3. Measured X-ray intensities, corrected f or background and scattered X-rays, are compared with a theoretical co ronal hole model. They are found to be broadly consistent with the mod el predictions for variation of intensity with height and for limb bri ghtening, although the electron density is lower than would be appropr iate for model predictions based on solar maximum densities. Electron temperatures estimated by the filter ratio method are also consistent with the model and with an in situ estimate of the maximum electron te mperature in the solar wind by the Ulysses ionic charge composition ex periment.