Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 71, p. 15-21 (2025)
SPECTRAL MANIFESTATIONS OF LOCAL MAGNETIC FIELD AMPLIFICATION AT THE CHROMOSPHERIC LEVEL OF A SOLAR FLARE
Vsevolod LOZITSKY, DSc (Phys. & Math.)
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
Ivan YAKOVKIN, PhD
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
Uliana PAVLICHENKO, Student
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
Abstract
Background. Current estimates of local magnetic fields in solar flares vary greatly and are in the range of 102–105 G. This is partly due to the fact that solar flares are actually very different in their physical characteristics, but also to the fact that different methods of measuring the magnetic field are not equivalent to each other, especially if the magnetic field is significantly inhomogeneous. The least studied based on direct methods are the magnetic fields in the solar chromosphere and corona. That is why the purpose of the presented work is new estimates of chromospheric magnetic fields in a solar flare based on the analysis of the characteristic features of the Zeeman effect in the Hα line and comparison of the corresponding results with those that follow from the study of the magnetic splitting of the photospheric line Fe I 6569.2 A.
Methods. The spectral-polarization method of measuring magnetic fields was used to process observations made with the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of the Taras Shevchenko National University of Kyiv. The Zeeman spectrogram of the solar flare of November 5, 2004 with a magnitude of M4.1/1B for the moment of 11:37 UT was scanned, and the blackening on the spectrogram was converted into intensity taking into account the characteristic curves of both the photographic material and the scanner itself. Estimates of the averaged and local magnetic fields in the solar flare region and in neighboring areas on the Sun were made on the basis of studying the splitting of the bisectors of the I ± V profiles of the above lines.
Results. Significant signs of altitudinal inhomogeneity of the magnetic field were found in the height range “photosphere – chromosphere”. This is indicated by the fact that the longitudinal component BLOS of the magnetic field was significantly different in value for the specified spectral lines. In the solar flare region, the corresponding intensities were greater by the Hα line than by the Fe I line, while outside the flare, their inverse ratio was obtained. In addition, the bisectors of the I ± V profiles in the Hα line everywhere in the studied regions do not correspond to a homogeneous magnetic field: they are mostly not parallel to each other, and in the flare region they have a maximum splitting near the centers of the emission profiles.
Conclusions. In the solar flare, the longitudinal component BLOS of the magnetic field is significantly (up to 2 times) larger by the Hα line than by the Fe I line, reaching a value of 1.5 kG in the region of maximum flare emission. Outside the flare, the ratio of the indicated intensities by the Hα and Fe I lines was obtained within 0.35–0.8. The non-parallelism of the bisectors in the Hα line indicates that the maximal magnetic fields at the chromospheric level were significantly stronger than 1.5 kG, and possibly reached the level of 104 G.
Key words
Sun, solar activity, solar flares, magnetic fields, bisectors of the Hα and Fe I line profiles, local magnetic field enhancement.
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