| 1. |
- Felipe, T., et al.
(författare)
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Three-dimensional structure of a sunspot light bridge
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 596
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Tidskriftsartikel (refereegranskat)abstract
- Context. Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation are fundamental problems in solar physics. Light bridges are commonly present during sunspot decay, but a comprehensive picture of their role in the removal of the photospheric magnetic field is still lacking. Aims. We study the three-dimensional configuration of a sunspot, and in particular, its light bridge, during one of the last stages of its decay. Methods. We present the magnetic and thermodynamical stratification inferred from full Stokes inversions of the photospheric Si I 10 827 angstrom and Ca I 10 839 angstrom lines obtained with the GREGOR Infrared Spectrograph of the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The analysis is complemented by a study of continuum images covering the disk passage of the active region, which are provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Results. The sunspot shows a light bridge with penumbral continuum intensity that separates the central umbra from a smaller umbra. We find that in this region the magnetic field lines form a canopy with lower magnetic field strength in the inner part. The photospheric light bridge is dominated by gas pressure (high-beta), as opposed to the surrounding umbra, where the magnetic pressure is higher. A convective flow is observed in the light bridge. This flow is able to bend the magnetic field lines and to produce field reversals. The field lines merge above the light bridge and become as vertical and strong as in the surrounding umbra. We conclude that this occurs because two highly magnetized regions approach each other during the sunspot evolution.
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| 2. |
- Joshi, Jayant, et al.
(författare)
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Upper chromospheric magnetic field of a sunspot penumbra : observations of fine structure
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 596
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The fine-structure of the magnetic field in a sunspot penumbra in the upper chromosphere is to be explored and compared to that in the photosphere. Methods. Spectropolarimetric observations with high spatial resolution were recorded with the 1.5-m GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The observed spectral domain includes the upper chromospheric Hei triplet at 10 830 angstrom and the photospheric Si I 10 827.1 angstrom and Ca I 10 833.4 angstrom spectral lines. The upper chromospheric magnetic field is obtained by inverting the Hei triplet assuming a Milne-Eddington-type model atmosphere. A height-dependent inversion was applied to the Si I 10 827.1 angstrom and Ca I 10 833.4 angstrom lines to obtain the photospheric magnetic field. Results. We find that the inclination of the magnetic field varies in the azimuthal direction in the photosphere and in the upper chromosphere. The chromospheric variations coincide remarkably well with the variations in the inclination of the photospheric field and resemble the well-known spine and interspine structure in the photospheric layers of penumbrae. The typical peak-to-peak variations in the inclination of the magnetic field in the upper chromosphere are found to be 10 degrees-15 degrees, which is roughly half the variation in the photosphere. In contrast, the magnetic field strength of the observed penumbra does not vary on small spatial scales in the upper chromosphere. Conclusions. Thanks to the high spatial resolution of the observations that is possible with the GREGOR telescope at 1.08 microns, we find that the prominent small-scale fluctuations in the magnetic field inclination, which are a salient part of the property of sunspot penumbral photospheres, also persist in the chromosphere, although at somewhat reduced amplitudes. Such a complex magnetic configuration may facilitate penumbral chromospheric dynamic phenomena, such as penumbral micro-jets or transient bright dots.
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| 3. |
- Lindner, P., et al.
(författare)
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Decay of a photospheric transient filament at the boundary of a pore and the chromospheric response
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 673
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Tidskriftsartikel (refereegranskat)abstract
- Context. The intermediate stages between pores and the formation of sunspots are a rare phenomenon and can be manifested as transient photospheric penumbral-like filaments. Although the magnetic field changes rapidly during the evolution of such filaments, they have not yet been shown to be connected to magnetic reconnection events.Aims. We characterize the evolution of transient photospheric filaments around a pore and search for possible signs of chromospheric responses.Methods. We analyzed observations of a pore in NOAA AR 12739 from the Swedish Solar Telescope, including the spectropolarimetric data of the Fe I 6173 Å and the Ca II 8542 Å line and spectroscopic data of the Ca II K 3934 Å line. The VFISV Milne-Eddington inversion code and the multi-line non-LTE inversion code STiC were utilized to obtain atmospheric parameters in the photosphere and the chromosphere.Results. Multiple filamentary structures of inclined magnetic fields are found in photospheric inclination maps at the boundary of the pore, although the pore had never developed a penumbra. One of the filaments shows a clear counterpart in continuum intensity maps, in addition to photospheric blueshifts. During its decay, a brightening in the blue wing of the Ca II 8542 Å line is observed. The Ca II K 3934 Å and the Ca II 8542 Å lines show complex spectral profiles in this region. Depth-dependent STiC inversion results using data from all available lines yield a temperature increase (roughly 1000 K) and bidirectional flows (magnitudes up to 8 km s−1) at log τ = −3.5.Conclusions. The temporal and spatial correlations of the decaying filament (observed in the photosphere) to the temperature increase and the bidirectional flows in the high photosphere and low chromosphere suggest that they are connected. We propose scenarios in which magnetic reconnection happens at the edge of a rising magnetic flux tube in the photosphere. This would lead to both the decay of the filament in the photosphere as well as the observed temperature increase and the bidirectional flows in the high photosphere and low chromosphere.
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