A Spectrum of the Sun from 168 to 700 A.

Abstract

A solar spectrum covering the range 168 to 700 A was obtained on June 21, 1961, from an Aerobee-High rocket. The instrument employed a 40-cm radius, 600-line/mm grating at 850 incidence. Stray light background was completely eliminated by introducing a self-supported film of aluminum, 1000 A thick, in front of the slit. This was opaque for A>850 A, but transmitted well from 700 A to about 170 A, the L2,3 edge of Al. An exposure of 110 sec made from 186 km to peak at 197 km and down to 178 km, showed approximately 50 emission lines between 167.9 and 310 A, in one or more orders. Twenty-five lines were photographed in three orders, and a line at 174.5 A in four. From 310 to 700 A only a few faint lines were recorded, because of strong attenuation at these wavelengths by N2 remaining overhead. Wavelengths have been established to 0.1 or 0.2 A. Surprisingly few lines agree with lines that are known in the laboratory, or with extrapolated lines. Heii (1) 304 A, and several higher members of the series are present. A line at 182.3 A appears to be Ha of Cvi. Ovi (4) 173.08, 172.93 A, are faintly present, but not resolved. The strong line at 284.3 A is identified as Fexv, as extrapolated by Edlen. The spectrum agrees well with the photoelectrically scanned spectrum obtained by Hinteregger (Astrophys. J. 132, 801, 1960). It is suggested that the resonance lines of Fcxvi, 336.2 A, 361.7 A, are present in the latter spectrum, but are probably absent from the photographic spectrum because of insufficient altitude. Most of the photographed lines, however, have not yet been identified, even though some are extremely intense.