Absolute solar ultraviolet intensities and their variations with solar activity. I - The wavelength region 1750-2100 A

Abstract

Absolute-calibrated high-resolution ultraviolet spectra from 1750 to 2100 A of the quiet Sun and a plage are presented. From these spectra, the intensity at the center of the disk, the average disk intensities, and the solar flux at 1 AU are derived. A comparison with other measurements shows that in this wavelength region most of the solar intensity measurements fall within an error limit of 120 percent. The variability of the solar flux in the band 1750-2050 A caused by active regions is estimated. A change of the sunspot number from 0 to 120 causes an approximate flux variation of 3 percent. The blackbody radiation temperature of a plage averaged over 2 x 60 arcsec in this wavelength region is 200 K higher than that of the quiet Sun. Subject headings: Sun: activity - Sun: plages - Sun: spectra - ultraviolet: spectra