Raio solar em frequências subterahertz e sua relação com a atividade solar

Abstract

The Sun emits radiation at several wavelengths of the electromagnetic spectrum. In the optical band, the solar radius is 696,000 km and this is what defines the photosphere, the visible surface of the Sun. However, as the altitude increases, the dominant electromagnetic radiation is produced at other frequencies, causing the solar radius to change as function of wavelength. We measure the solar radius at the subterahertz frequencies of 0,212 and 0,405 THz – i.e., the altitude where these emissions are generated – and also analyse the radius variation over the 11-year solar activity cycle. These measurements enable a better understanding of the solar atmosphere and the radius dependence on the solar cycle, is a good indicator of the changes that occur in the atmospheric structure. For this, we used radio maps of the solar disk for the period between 1999 and 2016, reconstructed from daily scans made by the Solar Submillimeter-wave Telescope (SST), installed at El Leoncito Astronomical Complex (CASLEO), at Argentinean Andes. At both frequencies our measurements yield a radius of 966,′′5 with dispersion of ±2,′′8 for 0,212 THz and ±2,′′7 for 0,405 THz. This implies a height of 5.0 ± 2.0 × 106 m above the photosphere. Furthermore, we also observed strong anti-correlation between radius variation and solar activity at both frequencies.