NEW RADIOMETRIC VALUES OF THE SOLAR ULTRAVIOLET CONTINUUM RADIATION FROM 1500-ANGSTROM TO 1700-ANGSTROM

A high-resolution stigmatic spectrometer, the High Resolution Telescop e and Spectrograph (HRTS), has been calibrated against broad-band irra diance measurements of the Sun with the Solar Ultraviolet Irradiance M onitor (SUSIM) and the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE), resulting in a new value for the radiance of the solar UV continuum from 1500 to 1700 angstrom. Previous HRTS results were based on a comparison with the Skylab SO82B calibration rocket, CALROC, and agreed, within the stated accuracy of +/- 25%, with other independent ly calibrated UV radiance measurements over the last 20 years. The new calibration increases the derived radiance in this wavelength range b y a factor of 1.35-1.5 over previous measurements. The difference is s ystematic over the wavelength range and cannot be explained by contrib utions to the irradiance from spectral lines or enhanced emission in a ctive regions. The new radiance values are significant for solar atmos pheric models as well as for related studies of stellar models, since the radiance at these wavelengths reflects the value of the minimum te mperature at the top of the photosphere.