Observations of the continuum radio emission from the undisturbed Sun at a wavelength of 8.7 meters

Abstract

We have mapped the continuum emission from the undisturbed Sun at a wavelength of 8.7 m during 1981-1985 using the large decameter-wave radio telescope at Gauribidanur, India with a resolution of 26 x 38 arc min. During the period August 6-30, 1983, the Sun was exceptionally quiet at meter and decameter wavelengths, and we were able to make maps on several consecutive days. On these days the position of the centroid of the radio Sun agreed quite closely with the center of the optical Sun indicating that there is very little or no contribution from active regions. But the observed peak brightness temperature varied from 100,000 to 700,000 K. The half-power widths of the brightness distribution were in the range of 3 to 4 solar radii. The variations of the brightness temperature and the half-power widths are not correlated. It is therefore suggested that the variations of the brightness temperature are not caused by uniform density variations or due to scattering by an irregular corona.