Spectral Study of Ellerman Bombs. Photosphere

Abstract

The results of analysis of spectral observations of two Ellerman bombs (EB-1 and EB-2), which were formed and have evolved in the area of emerging magnetic flux in active region (AR) NOAA 11024, are presented. Spectral data with high spatial and temporal (approximately 3 s) resolution were obtained using the THEMIS French–Italian solar telescope on July 4, 2009. The observation duration was 20 min. The spectral region of λ ≈ 630 nm with photospheric lines forming in a wide altitude range (neutral iron lines Fe I λ 630.15, 630.25, and 630.35 nm and titanium line Ti I λ 630.38 nm) was examined. The brightness of EB-1 decreased in the process of observations, while the brightness of EB-2 increased. The profiles of metal lines determined at different stages of EBs evolution were asymmetric. This asymmetry was more pronounced in lines that had formed in the lower photospheric layers and often had profiles with several components. The half-width of profiles increased with a reduction in their central depth. The variation of central intensities of Fraunhofer lines in the spectra of EBs and their vicinity at different stages of EB evolution was analyzed. The EBs formed in intergranular lanes. An increase in the core intensity of all the studied photospheric lines was correlated spatially with an increase in the wings intensity of the Hα line. Brightness variations at all photospheric levels were of an oscillatory nature with an interval of 1–5 min. The observed temporal variations of Fraunhofer line intensities in the spectra of the studied AR section suggest that the emergence of the new magnetic flux induced consecutive magnetic reconnections in the EB-1 region, the excitation propagated along a magnetic loop and initiated the formation of EB-2, and the two bombs then evolved as a physically connected pair.