Highlights of solar observations with two Brazilian radio telescopes

Abstract

Solar emission may be divided into three time scales. A slowly varying component that varies periodically with the 11 years solar Activity Cycle. The quiescent component, varying on timescale of weeks is related to the appearance of active regions on the solar surface. Finally, the third component, related to solar flares and coronal mass ejections, varies on timescales of second to hours. All three components are observed at radio wavelengths and produced by different emission mechanisms. At microwave and millimeter wavelengths, the quiet Sun emission is produced by bremsstrahlung from thermal electrons. The height on the solar atmosphere were this emission is produced can be determined from center-to-limb observations at multiple radio frequencies. The quiescent radio emission from the active regions, brighter than the surrounding solar disk, is dominated by thermal gyro-resonance at microwaves and by 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).