Spectral investigations of Solar magnetic fields in Astronomical observatory of Taras Shevchenko National University of Kyiv in 1981–1986

Abstract

In the second five-year period of spectral studies of solar magnetic fields in Astronomical Observatory of the Taras Shevchenko National University of Kyiv (1981-1986), a number of important and interesting scientific results were obtained, which mainly concern magnetic fields in solar flares and beyond. In particular, based on the analysis of the Echelle Zeeman spectrograms obtained at the observatory during the international FBS/SERF program, it was shown that the effect of the “magnetic transient” according to the data of the BBSO observatory probably has a non-magnetic nature. Also, “kilogauss” magnetic fields (1–3 kG) were discovered and previously studied in solar flares, more precisely, in the region of intense emission in strong FeI lines, which is formed in the upper photosphere and the temperature minimum zone. For a section of the photosphere of the active region without solar flares, observational evidences of the discreteness of local magnetic field intensities were obtained, which turned out to be equal to ≈ 4, 7 and 13 kG. For the same area, indications of the existence of a moderately strong (up to ~ 1 kG) background magnetic field of mixed polarity were found. It was possible to explain these observational data theoretically within the framework of the linear force-free MHD model, according to which the central parts of small-scale magnetic structures with strong and discrete fields are surrounded by concentric regions with a sign-changing and weaker magnetic field. In a solar flare, a sign-changing height gradient of the longitudinal magnetic field was discovered and investigated, one of the reasons for which may be a significant deformation of the magnetic field of the shear type, which gradually weakened towards the end of the flare. In all the above-mentioned questions, the “last word” has not yet been said – they require thorough research in the future.