New measurements of the solar disk-center spectral intensity in the near IR from 645 nm to 1070 nm

Abstract

At the high-altitude station on Terskol Peak (central Caucasus, 3100 m) by the Main Astronomical Observatory of the National Academy of Sciences of the Ukraine in 1992, spectral measurements of the solar disk-center intensity for the near IR region were performed. These measurements are a continuation of the solar absolute spectral energy distribution investigation programme. Data published earlier (Burlov-Vasiljev, Gurtovenko, and Matvejev, 1995a) are expanded now in the long-wave spectral region up to 1070 nm. The measurements were made with the specialized solar telescope SEF-1. The method of comparison of the solar disk-center brightness with the brightness of the calibrated region of a standard ribbon tungsten lamp was used. The atmospheric extinction was taken into account with Bouger's 'long' method accompanied by the parallel-independent control of atmospheric stability. The uncertainty of the absolute solar disk-center intensity values is estimated to be 2% in regions free from the strong telluric absorption of atmosphere oxygen and water vapour. In these regions an additional reduction was carried out, which was derived from the synthetic atmospheric absorption spectra computed on the basis of the molecular parameter data and the standard model of the Earth's atmosphere. The 1-nm integrals of the disk-center radiance in the wavelength range λλ650-1070 nm, which are established on 5-day measurements in March-October 1992, are given. With the help of the solar disk-darkening coefficients, the solar flux values at 1 AU are available. The measured 1-nm integrals were used for the high-resolution solar spectral atlas calibration in order to locate the solar continuum in absolute units. A comparison is made of the data obtained with the data by Neckel and Labs (1984) and data of some other authors.