Physical conditions in m6.4/3n solar flare of 19 july 2000

Abstract

We investigate the solar flare on July 19, 2000 of M6.4/3N class, which arose in the active region NOAA 9087. Echelle Zeeman spectrograms of this flare were obtained at the horizontal solar telescope of the Astronomical Observatory of the Taras Shevchenko National University of Kyiv. The effective magnetic field B-eff was measured using spectral lines FeI 6301.5, FeI 6302.5 and H-beta. It turned out that in the brightest place of the flare, which was projected onto a small sunspot of N magnetic polarity, B-eff by all three above-named lines are close to each other and correspond to 1.0-1.2 kG. At the same time, the module of magnetic field strength at the level of formation of FeI 6302.5 was within the range of 1.6-2.6 kG. The features of the bisectors of I +/- V profiles of FeI 6301.5 line indicate a simple one-component magnetic field structure at the level of the middle photosphere under the flare. The semi-empirical model of the photospheric layers was constructed on the basis of the observational profiles of Stokes I of Fe I 5123.7 and 5434.5 lines by solving the inverse problem of non-equilibrium transfer of radiation using Tikhonov's stabilizers. It turned out that for the temperature distribution with height, the deviation from the LTE is already significant for the layers of the lower photosphere corresponding to the heights h >= 0 (that is, tau(5) <= 1). In the entire thickness of the photosphere (h = 0 - 500 km), the temperature in the flare is lowered compared to the undisturbed atmosphere, whereas for h > 500 km it is slightly elevated. The microturbulent velocity is raised at altitudes of h = 200 500 km, while at altitudes of h < 200 km it is lowered. The obtained results indicate that the upper photosphere and the lower chromosphere are significantly disturbed during a solar flare, even when the magnetic field in the lower layers (the middle photosphere) is quasi-homogeneous.