Experience in Studying the Near-Limb Zone of the Sun Based on Observations on Large Full-Rotation Radio Telescopes

N. A. Topchilo, V. G. Nagnibeda, N. G. Peterova

Transactions of IAA RAS, issue 65, 42–53 (2023)

DOI: 10.32876/ApplAstron.65.42-53

Keywords: radio telescope, radio map, active region, prominence, coronal mass ejection, radio radius of the Sun, polarization of radio emission, magnetic field

Abstract

Observations of the near-limb zone are of particular importance for the study of the solar atmosphere, since they provide information about its altitudinal structure. The microwave-observable chromosphere, transition region, and lower corona contain a large number of non-stationary 3D structures of various types and sizes, the difficulties of studying which increase significantly in this zone due to the presence of a strong general height brightness gradient. So, the method of raster mapping commonly used in radio observations leads to large errors when identifying sources on the limb of the Sun. The purpose of this work is to demonstrate the possibilities of improving the accuracy of near-limb observations on existing large full-rotation antennas. Previously, when using similar radio telescopes with a characteristic beam size of a few arc minutes, another method was proposed to eliminate these errors-circular scanning, when the telescope performs circular scans relative to the center of the Sun. This and other developed methods were implemented in the early 80s on the RT-22 radio telescope of the Lebedev Physical Institute, and in the late 80s on the RT-22 CrAO. Similar methods have been used for many years to map the Sun with the RT-7.5 radio telescope of the Bauman Moscow State Technical University on waves 3.4 and 2.5 mm. To demonstrate the advantages of new methods, the article presents the results of observations of solar prominences behind the solar limb and filaments on the disk in near-limb regions at wavelengths of 8 mm and 1.35 cm, carried out in the 1980s and 1990s. Their positions, sizes along the limb, and heights, measured magnetic field. Cases of observations of the rise and destruction of prominences, as well as coronal mass ejections (CMEs) have been noted. The values of the radio radius of the Sun were measured. Based on our experience, we can conclude that the proposed methods can undoubtedly be implemented on radio telescopes included in the Quasar-KVO complex of the IAA RAS. A range of promising scientific problems on solar topics and requirements for the organization of observations and their software are determined.

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