Very Large Array (V.L.A.) Observations of Solar Active Regions.

Abstract

Abstract : High resolution radio wavelength observations of solar active regions indicate ever present, fine scale features whose high degree of circular polarization reflects the magnetic field structure in the solar corona. Changes in this structure may trigger major flare eruptions in solar active regions which create geophysical disturbances and disrupt terrestrial communication and surveillance systems. In this paper we discuss the basic techniques of using the Very Large Array (V.L.A.) to obtain radio wavelength observations (6 cm) maps of solar active regions. It is shown that the V.L.A. coverage in the u-v plane (the Fourier plane of the active region's brightness distribution) is much more complete than the u-v coverage available with other synthesis telescopes or with interferometers with east-west baseline configurations. Calibration procedures for V.L.A. observations of the Sun are discussed, and maps of two solar active regions are presented. For the first time radio wavelength maps of coronal magnetic field structures have been obtained with angular resolutions comparable to those obtained at optical wavelengths when viewing the cooler, lower lying photosphere.