1.3.7.4. Sun and near-Earth space, solar-terrestrial connections
   1.3.7.6. Development of methods of ground-based and extra-atmospheric astronomy
   Section 3. Sun; Section 11. Radio telescopes and methods

    Ovchinnikova N.E., Bogod V.M., Lebedev M.K., Ripak A.M., Storozhenko A.A., Kurochkin E.A. (SAO RAS)

    When observing the Sun with the RATAN-600 using a new high-speed spectral polarimetric complex with a frequency resolution of 0.12–8 MHz and a time resolution of 8 ms in the range of 1–3 GHz in the radio emission spectra of individual active regions (AR), an absorption line was discovered on the Sun in the frequency range of 1.5–1.65 GHz near the hydroxyl absorption line (1.7 GHz). The absorption was observed only in the emission of those ARs that were overlapped with a cool filament visible in the H-α images or on the limb in the presence of a prominence, where the existence of a hydroxyl molecule is potentially possible. The line shape corresponds to the estimated model calculations for conditions in a cool filament in the solar corona (7500 K, ~10^-6 atm) taking into account the instrumental function of the 1–3 GHz spectral polarimetric complex (without taking into account the displacement due to a magnetic field). The discovery of molecular lines in the solar corona may indicate the nature of its heating and the stability of its temperature balance.

Fig. 1. Emission spectrum of of NOAA 13258 at the base of a large vortex-like prominence in the western limb of the Sun, in the guiding mode in s.f.u. units accumulated over ten minutes with a frequency resolution of 4 MHz.

Fig. 2. Estimation model of the transmission function of the hydroxyl molecule in the region of 0.04–0.06 cm-1: at the top – taking into account the instrument function of the receiving complex, at the bottom – without taking into account the instrument function.

The work was carried out within the framework of the research plan № 121101300033-9.

Published:
1. V.M. Bogod, M.K. Lebedev. Detection of the hydroxyl (OH) absorption line in the radio emission of the solar corona. Solar and solar-terrestrial physics – 2023, St. Petersburg, Pulkovo, October 9–13. p. 245–248. DOI: 10.31725/0552-5829-2023-245-248
2. V.M. Bogod, M.K. Lebedev, N.E. Ovchinnikova, A.M. Ripak, and A.A. Storozhenko. Spectroradiometry of the Solar Corona on the RATAN-600. Cosmic Research, 2023, Vol. 61, No. 1, pp. 27–33. DOI: 10.1134/S001095252301001X