Evolution of solar flare SOL 2013-05-17: analysis of optical spectra (Balmer series) and quasiperiodic pulsations

Abstract

This work aims to study the behavior of radiation intensity curves in the Hε, Hβ, and Hα lines during the development of a flare and compare the results with calculated values. Observations were carried out with the horizontal solar telescope HSFA-2 (Ondrejov Observatory). The 2013-05-17 M3.2 flare in the NOAA AR 11748 was selected for processing, and the absolute values of fluxes in the spectral lines were determined. It is shown that the model of heating of the chromospheric gas by the flow of magnetohydrodynamic waves from the convective zone and its ionization and excitation by the flow of suprathermal particles from the corona satisfies the observations. Calculations are performed in hydrogen lines, taking into account the main processes that determine the radiation of gas, opaque in spectral lines. The flat decrement of the Balmer series indicates the inhomogeneity of the radiating region along the vertical. The search for quasiperiodic pulsations showed that in this flare they were found only in the Hα line with a significance level of 95%. They are absent in other spectral ranges.