Measurement of Vector Magnetic Field in a Flare kernel with a Spectropolarimetric Observation in He I 10830 A

A flare kernel associated with a C4 class flare was observed in a spectral window including the He I triplet 10830 A and Si I 10827 A with a spectropolarimeter on the Domeless Solar Telescope at Hida Observatory on August 9th, 2015. Observed Stokes profiles of the He I triplet in the flare kernel in its post-maximum phase are well reproduced through

Determining the dynamics and magnetic fields in He I 10830 r{A} during a solar filament eruption

We investigate the dynamics and magnetic properties of the plasma, such as line-of-sight velocity (LOS), optical depth, vertical and horizontal magnetic fields, belonging to an erupted solar filament. The filament eruption was observed with the GREGOR Infrared Spectrograph (GRIS) at the 1.5-meter GREGOR telescope on 2016 July 3. Three consecutive full-Stokes slit-spectropolarimetric scans in the He I 10830 r{A} spectral range were acquired. The Stokes I profiles were classified using the machine learning k-means algorithm and then inverted with different initial conditions using the HAZEL code. The erupting-filament material presents the following physical conditions: (1) ubiquitous upward motions with peak LOS velocities of ~73 km/s; (2) predominant large horizontal components of the magnetic field, on average, in the range of 173-254 G, whereas the vertical components of the fields are much lower, on average between 39-58 G; (3) optical depths in the range of 0.7-1.1. The average azimuth orientation of the field lines between two consecutive raster scans (<2.5 minutes) remained constant. The analyzed filament eruption belonged to the fast rising phase, with total velocities of about 124 km/s. The orientation of the magnetic field lines does not change from one raster scan to the other, indicating that the untwisting phase has not started yet. The untwisting seems to start about 15 min after the beginning of the filament eruption.

Formation and evolution of an active region filament

Several scenarios explaining how filaments are formed can be found in literature. In this paper, we analyzed the observations of an active region filament and critically evaluated the observed properties in the context of current filament formation models. This study is based on multi-height spectropolarimetric observations. The inferred vector magnetic field has been extrapolated starting either from the photosphere or from the chromosphere. The line-of-sight motions of the filament, which was located near disk center, have been analyzed inferring the Doppler velocities. We conclude that a part of the magnetic structure emerged from below the photosphere.

Line formation of He I D3 and He I 10830 {AA} in a small-scale reconnection event

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.

Formation of an active region filament driven by a series of jets

We present a formation process of a filament in active region NOAA 12574 during the period from 2016 August 11 to 12. Combining the observations of GONG H$alpha$, Hida spectrum and SDO/AIA 304 A, the formation process of the filament is studied. It is found that cool material ($Tsim10^4$ K) is ejected by a series of jets originating from the western foot-point of the filament. Simultaneously, the magnetic flux emerged from the photosphere in the vicinity of the western foot-point of the filament. These observations suggest that cool material in the low atmosphere can be directly injected into the upper atmosphere and the jets are triggered by the magnetic reconnection between pre-existing magnetic fields and new emerging magnetic fields. Detailed study of a jet at 18:02 UT on August 11 with GST/BBSO TiO observations reveals that some dark threads appeared in the vicinity of the western foot-point after the jet and the projection velocity of plasma along the filament axis was about 162.6$pm$5.4 km/s. Using with DST/Hida observations, we find that the injected plasma by a jet at 00:42 UT on August 12 was rotating. Therefore, we conclude that the jets not only supplied the material for the filament, but also injected the helicity into the filament simultaneously. Comparing the quantity of mass injection by the jets with the mass of the filament, we conclude that the estimated mass loading by the jets is sufficient to account for the mass in the filament.