X-Ray Emission Line Spectrum of a Coronal Active Region

Abstract

Two slitless Bragg spectrometers were successfully used on a Sun-pointed Skylark rocket flight (SL 304) on May 5, 1966, to measure the solar X-ray emission below 25 Å. The crystals were of potassium acid phthallate (KAP), with a lattice constant of 13.3 Å, and photons were detected with thin plastic window proportional counters. The rocket launch took place at 0414 h (U.T.) during a period of relatively quiet solar activity. In particular, no solar flares have been reported in a period of several hours around the time of launching. Solar pointing was achieved approximately 100 sec after launch and was maintained until re-entry 274 sec later. The apogee of the rocket was 181 km, giving a negligible atmospheric attenuation, for the X-ray wavelengths being measured, throughout most of the controlled flight. Four spectral scans over the wavelength band 11–25 Å were obtained. The data have been reduced by computer. A full analysis is still proceeding, but this communication reports the emission line identifications so far obtained, several not having previously been seen in the solar spectrum.