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Register a new userHigh resolution He I 10830 AA narrow-band imaging of an M-class flare. I - analysis of sunspot dynamics during flaring
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In this paper, we report our first-step results of high resolution He,textsc{i} 10830 AA narrow-band imaging (bandpass: 0.5 {AA}) of an M1.8 class two-ribbon flare on July 5, 2012. The flare was observed with the 1.6 meter aperture New Solar Telescope at Big Bear Solar Observatory. For this unique data set, sunspot dynamics during flaring were analyzed for the first time. By directly imaging the upper chromosphere, running penumbral waves are clearly seen as an outward extension of umbral flashes, both take the form of absorption in the 10830 AA narrow-band images. From a space-time image made of a slit cutting across a flare ribbon and the sunspot, we find that the dark lanes for umbral flashes and penumbral waves are obviously broadened after the flare. The most prominent feature is the sudden appearance of an oscillating absorption strip inside the ribbon when it sweeps into the sunspots penumbral and umbral regions. During each oscillation, outwardly propagating umbral flashes and subsequent penumbral waves rush out into the inwardly sweeping ribbon, followed by a returning of the absorption strip with similar speed. We tentatively explain the phenomena as the result of a sudden increase in the density of ortho-Helium atoms in the area of the sunspot being excited by the flares EUV illumination. This explanation is based on the observation that 10830 AA absorption around the sunspot area gets enhanced during the flare. Nevertheless, questions are still open and we need further well-devised observations to investigate the behavior of sunspot dynamics during flares.
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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.
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.
We investigated the reliability of our silicon atomic model and the influence of non-local thermodynamical equilibrium (NLTE) on the formation of neutral silicon (Si I) lines in the near-infrared (near-IR) H-band. We derived the differential Si abundances for 13 sample stars with high-resolution H-band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), as well as from optical spectra, both under local thermodynamical equilibrium (LTE) and NLTE conditions. We found that the differences between the Si abundances derived from the H-band and from optical lines for the same stars are less than 0.1 dex when the NLTE effects included, and that NLTE reduces the line-to-line scatter in the H-band spectra for most sample stars. These results suggest that our Si atomic model is appropriate for studying the formation of H-band Si lines. Our calculations show that the NLTE corrections of the Si I H-band lines are negative, i.e. the final Si abundances will be overestimated in LTE. The corrections for strong lines depend on surface gravity, and tend to be larger for giants, reaching ~ -0.2 dex in our sample, and up to ~ -0.4 dex in extreme cases of APOGEE targets. Thus, the NLTE effects should be included in deriving silicon abundances from H-band Si I lines, especially for the cases where only strong lines are available.
Understanding the dynamics and kinematics of out-flowing atmospheres of hot and warm exoplanets is crucial to understanding the origins and evolutionary history of the exoplanets near the evaporation desert. Recently, ground based measurements of the meta-stable Helium atoms resonant absorption at 10830 AA~has become a powerful probe of the base environment which is driving the outflow of exoplanet atmospheres. We report evidence for the He I 10830 AA~in absorption (equivalent width $sim$ $0.012 pm 0.002$ AA) in the exosphere of a warm Neptune orbiting the M-dwarf GJ 3470, during three transits using the Habitable Zone Planet Finder (HPF) near infrared spectrograph. This marks the first reported evidence for He I 10830 AA, atmospheric absorption for a planet orbiting an M-dwarf. Our detected absorption is broad and its blueshifted wing extends to -36 km/sec, the largest reported in the literature to date. We modelled the state of Helium atoms in the exosphere of GJ3470b based on assumptions on the UV and X-ray flux of GJ 3470, and found our measurement of flux-weighted column density of meta-stable state Helium $(N_{He^2_3S} = 2.4 times 10^{10} mathrm{cm^{-2}})$, derived from our transit observations, to be consistent with model, within its uncertainties. The methodology developed here will be useful to study and constrain the atmospheric outflow models of other exoplanets like GJ 3470b which are near the edge of the evaporation desert.
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