Study of Cooling Processes during the Decay Phase of Solar and Stellar Flares

Abstract

The work is devoted to the study of cooling processes and energy loss during the decay phase of flare. During this phase, various wave processes can occur simultaneously with the processes of cooling and energy loss, leading to additional energy release, which makes it an interesting object of research. It is assumed that the cooling of the flare plasma during the decay phase occurs due to two processes—thermal conduction and radiation losses. At the beginning, the process of thermal conduction dominates, and then comes the complete dominance of the process of radiation losses. We have analyzed the average time profiles of solar flares in the SDO/AIA bands 304 Å, 1600 Å, and 1700 Å and the average time profile of a flare in white light on the dwarf of spectral class M4. To describe the time profiles, an analytical model based on known formulas of temperature behavior has been proposed. The results of the analysis using the developed model showed that the domination of the cooling process due to radiation losses for the 304 Å SDO/AIA band occurs earlier than it is determined in the standard model. For other spectral bands, the process of radiation losses dominates the decay phase almost all the time. Comparison of the results obtained for flares on the red dwarf M4 and in solar flares showed that the cooling processes in solar and stellar flares are similar and depend on the structure of the atmosphere. The proposed analytical model can be used for separation of the classical form decay process and the energy release processes overlapped on it.