The brightness temperature of the Sun constitutes a basic property of the solar atmosphere. The main emission mechanism of the Sun at millimeter and submillimeter wavelengths is thermal free–free emission from the chromosphere, which is an atmospheric layer with a temperature ranging between 6000 to 20,000 K. The opacity of thermal free–free emission depends on the temperature and density in the emission region. In addition, the Rayleigh– Jeans law is applicable to this wavelength range (Dulk, 1985); thus, we can develop vertical models of the chromospheric density and temperature distributions based on the brightness temperature spectrum of the thermal free–free emission. However, large millimeter and submillimeter telescopes are not always able to observe the Sun. The purpose of this study is to establish observation and calibration sequences of the solar brightness temperatures at millimeter wavelengths using single-dish telescopes.
Solar Observation by Large Millimeter Telescope
In this study, we demonstrate solar-observation sequences at millimeter wavelengths using the Nobeyama 45 m telescope. This telescope is a ground-based, millimeter-wavelength radio telescope operated by the Nobeyama Radio Observatory (NRO). The typical spatial resolution of this telescope is 15’’ at 115 GHz. The observation sequences are summarized as follows;
We tuned the superconductor–insulator–superconductor (SIS) receiver ...