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تسجيل مستخدم جديدLine formation of He I D3 and He I 10830 {AA} in a small-scale reconnection event
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Aims. We aim to explain line formation of He I D3 and He I 10830 {AA} in small-scale reconnection events. Methods. We make use of a simulated Ellerman bomb (EB), present in a Bifrost-generated radiative Magnetohydrodynamics (rMHD) snapshot. The resulting He I D3 and He I 10830 AA line intensities are synthesized in 3D using the non-LTE Multi3D code. We compare the synthetic helium spectra with observed SST/TRIPPEL raster scans of EBs in He I 10830 AA and He I D3. Results. Emission in He I D3 and He I 10830 AA is formed in a thin shell around the EB at a height of $sim 0.8$ Mm while the He I D3 absorption is formed above the EB at $sim 4$ Mm. The height at which the emission is formed corresponds to the lower boundary of the EB, where the temperature increases rapidly from $6cdot 10^3$ K to $10^6$ K. The opacity in He I D3 and He I 10830 AA is generated via photoionization-recombination driven by EUV radiation that is locally generated in the EB at temperatures in the range of $2cdot 10^4 - 2cdot 10^6$ K and electron densities between $10^{11}$ and $10^{13}$ cm$^{-3}$. The synthetic emission signals are a result of coupling to local conditions in a thin shell around the EB, with temperatures between $7cdot 10^3$ and $10^4$ K and electron densities ranging from $sim 10^{12}$ to $10^{13}$ cm$^{-3}$. Hence, both strong non-LTE as well as thermal processes play a role in the formation of He I D3 and He I 10830 AA in the synthetic EB/UV burst that we studied. Conclusions. In conclusion, the synthetic He I D3 and He I 10830 AA emission signatures are an indicator of temperatures of at least $2cdot 10^4$ K and in this case as high as $sim 10^6$ K.
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