| 1. |
- Da Silva Santos, J. M., et al.
(författare)
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Subarcsecond Imaging of a Solar Active Region Filament With ALMA and IRIS
- 2022
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media SA. - 2296-987X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Quiescent filaments appear as absorption features on the solar disk when observed in chromospheric lines and at continuum wavelengths in the millimeter (mm) range. Active region (AR) filaments are their small-scale, low-altitude analogues, but they could not be resolved in previous mm observations. This spectral diagnostic can provide insight into the details of the formation and physical properties of their fine threads, which are still not fully understood. Here, we shed light on the thermal structure of an AR filament using high-resolution brightness temperature (Tb) maps taken with ALMA Band 6 complemented by simultaneous IRIS near-UV spectra, Hinode/SOT photospheric magnetograms, and SDO/AIA extreme-UV images. Some of the dark threads visible in the AIA 304 Å passband and in the core of Mg ii resonance lines have dark (Tb << 5,000 K) counterparts in the 1.25 mm maps, but their visibility significantly varies across the filament spine and in time. These opacity changes are possibly related to variations in temperature and electron density in filament fine structures. The coolest Tb values (<< 5,000 K) coincide with regions of low integrated intensity in the Mg ii h and k lines. ALMA Band 3 maps taken after the Band 6 ones do not clearly show the filament structure, contrary to the expectation that the contrast should increase at longer wavelengths based on previous observations of quiescent filaments. The ALMA maps are not consistent with isothermal conditions, but the temporal evolution of the filament may partly account for this.
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| 2. |
- Pietrow, Alexander G. M., 1991-
(författare)
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Physical properties of chromospheric features : Plage, peacock jets, and calibrating it all
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chromosphere is a complex and dynamic layer of the solar atmosphere, largely dominated by the local magnetic field configuration. It acts as an important interface between the photosphere below it and the hot corona above. However, studying this layer is not straightforward, as it is largely transparent in optical wavelengths. On top of that most of its observable radiation is formed in conditions far from thermodynamic equilibrium, and thus only partially sensitive to local plasma conditions. Observations of the active features found in the chromosphere such as plage, fibrils, and jets, are therefore more difficult to interpret than emission from active features in the photosphere.This thesis focuses on plage and peacock-jets, two types of chromospheric features. Additionally, I study the quiet solar atmosphere for calibration purposes. In all three cases, I utilize high-resolution spectral and spectro-polarimetric data from the Swedish 1-m Solar Telescope (SST) in order to constrain the physical parameters of these regions and to create high-resolution reference profiles of the quiet regions.In the first paper, the magnetic field vector of a plage region is inferred using STiC, a spectro-polarimetric inversion code, which is achieved after applying several methods to improve the signal-to-noise ratio.In the second paper, a peacock jet near an X9.3-class flare is studied. The expanding flare ribbon moves under the jet and inhibits new material from being accelerated upwards. This coupled with back-lighting from the heavily broadened line profile of the flare ribbon that can be approximated as quasi-continuum, allowed us to estimate its density and mass by using a cloud model. The third paper is an observational study of the center-to-limb variations of ten spectral lines commonly used for solar diagnostics.
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