Highlights of Solar Observations with Two Brazilian Radio Telescopes

Abstract

Solar radio emission originates from the solar atmosphere, and basically consists of emission from the quiet Sun, active regions, and flares. The slowly varying emission from the quiet solar atmosphere follows the periodicity of the 11 years Solar Activity Cycle. Active regions on the solar surface produce emission that varies on timescale of days or weeks, also known as the quiescent component. Finally, solar bursts are sudden increase of the emission on timescales of seconds to hours resulting from solar magnetic activity. These three components are produced by different emission mechanisms at distinct radio wavelengths. At microwave and millimeter wavelengths, the quiet Sun emission is produced by bremsstrahlung from thermal electrons. The height on the solar atmosphere where the submillimeter emission is mostly produced was determined to be ≤ 3000 km from center-to-limb observations at multiple radio frequencies. The quiescent radio emission from the active regions, usually brighter than the surrounding solar disk, is dominated by thermal gyro- resonance at microwaves and by optically thick thermal bremsstrahlung at millimetric and submillimetric waves. Lastly, gyro-synchrotron radiation from non-thermal electrons is responsible for the flare emission at high radio frequencies. In this review, the discoveries about the Sun obtained from two Brazilian radio telescopes installed at CASLEO (Argentina, the Submillimeter Solar Telescope (SST, 212 and 405 GHz) and the POlarization Emission of Millimeter Solar Activity (POEMAS, 45 and 90 GHz) are presented. The main result from SST was the discovery of a new spectral component increasing toward even higher frequencies.