Soft X-Ray Images of the Solar Corona With a Normal-Incidence Cassegrain Multilayer Telescope

Abstract

High resolution images of the sun in the soft x-ray/extreme ultraviolet (XUV) regime have been obtainec with normal-incidence Cassegrain multilayer telescopes for the first time. The inherent energy selective property of multilayer-coated optics allowed distinct groups of emission lines to be isolated in the solar corona and the transition region. The sounding rocket borne soft x-ray telescopes [1] were launched on October 23, 1987. In addition to the Cassegrain telescopes, which provided images in bands centered at 173 Å and 256 Å, the payload contained concave spherical mirror multilayer telescopes operating at 44 Å and 256 Å, and convex multilayer mirrors which magnified and spectroscopically analyzed the image produced by a grazing-incidence primary mirror. The images obtained with the Cassegrain telescope operated in the bandpass centered at 173 Å, which is dominated by emission from the ions Fe IX and Fe X, are presented here. This emission is from coronal plasma in the temperature range 0.8 x 106 to 1.3 x 106 K. The images have angular resolution of ~1.0 to 1.5 arc seconds, and show no degradation due to x-ray scattering. Many features of coronal structure, including magnetically confined loops of hot plasma, coronal plumes, polar coronal holes, faint structures on the size scale of supergranulation and smaller, and features due to overlying cool prominences are visible in the images. The density structure of polar plumes has been derived from the observations. The images were recorded on a new type of XUV sensitive film. Our 64 second exposure of the sun in the bandpass 171 - 175 Å is shown below.