| 1. |
- Kiselman, Dan, 1963-
(författare)
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Extremt rymdväder
- 2018
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Ingår i: Fysikaktuellt. - 0283-9148. ; :1, s. 24-26
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 2. |
- Kiselman, Dan, 1963-, et al.
(författare)
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Is the solar spectrum latitude-dependent? An investigation with SST/TRIPPEL
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 535, s. A14-
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Tidskriftsartikel (refereegranskat)abstract
- Context. In studies of the solar spectrum compared to spectra of solar twin stars, it has been found that the chemical composition of the Sun seems to depart systematically from those of the twins. One possible explanation could be that the effect is caused by the special aspect angle of the Sun when observed from Earth compared with the aspect angles of the twins. This means that a latitude dependence of the solar spectrum, even with the heliocentric angle constant, could lead to the observed effects. Aims. We explore a possible variation in the strength of certain spectral lines that are used in the comparisons between the composition of the Sun and the twins at loci on the solar disk with different latitudes but at constant heliocentric angle. Methods. We use the TRIPPEL spectrograph at the Swedish 1-m Solar Telescope on La Palma to record spectra in five spectral regions to compare different locations on the solar disk at a heliocentric angle of 45◦ . Equivalent widths and other parameters are measured for fifteen different lines representing nine atomic species. Spectra acquired at different times are used in averaging the line parameters for each line and observing position. Results. The relative variations in equivalent widths at the equator and at solar latitude ∼45◦ are found to be less than 1.5% for all spectral lines studied. Translated into elemental abundances as they would be measured from a terrestrial and a hypothetical pole-on observer, the difference is estimated to be within 0.005 dex in all cases. Conclusions. It is very unlikely that latitude effects could cause the reported abundance difference between the Sun and the solar twins. The accuracy obtainable in measurements of small differences in spectral line strengths between different solar disk positions is very high, and can be exploited in studies of, e.g. weak magnetic fields or effects of solar activity on atmospheric structure.
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| 3. |
- Pietrow, Alexander G. M., 1991-, et al.
(författare)
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Center-to-limb variation of spectral lines and continua observed with SST/CRISP and SST/CHROMIS
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 671
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Tidskriftsartikel (refereegranskat)abstract
- Context. Observations of center-to-limb variations (CLVs) of spectral lines and continua provide a good test for the accuracy of models with a solar and stellar atmospheric structure and spectral line formation. They are also widely used to constrain elemental abundances, and are becoming increasingly more important in atmospheric studies of exoplanets. However, only a few such data sets exist for chromospheric lines.Aims. We aim to create a set of standard profiles by means of mosaics made with the CRISP and CHROMIS instruments of the Swedish 1-m Solar Telescope (SST), as well as to explore the robustness of said profiles obtained using this method.Methods. For each spectral line, we used a mosaic that ranges from the center to the limb. Each of these mosaics were averaged down to 50 individual spectral profiles and spaced by 0.02 in the μ scale. These profiles were corrected for p-mode oscillations, and their line parameters (equivalent width, line shift, full-width at half-maximum, and line depth) were then compared against literature values whenever possible.Results. We present a set of 50 average profiles that are spaced equidistantly along the cosine of the heliocentric angle (μ) by steps of 0.02 for five continuum points between 4001 and 7772 Å, as well as ten of the most commonly observed spectral lines at the SST (Ca II H & K, Ηβ, Mg I 5173 Å, C I 5380 Å, Fe I 6173 Å, Fe I 6301 Å, Ha, O I 7772 Å, and Ca II 8542 Å).Conclusions. The CLV of line profiles and continua are shared in the CDS as machine readable tables, providing a quantitative constraint on theoretical models that aim to model stellar atmospheres.
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| 4. |
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| 5. |
- Pietrow, Alexander G. M., 1991-, et al.
(författare)
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Physical properties of a fan-shaped jet backlit by an X9.3 flare
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 659
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Tidskriftsartikel (refereegranskat)abstract
- Context. Fan-shaped jets sometimes form above light bridges and are believed to be driven by the reconnection of the vertical umbral field with the more horizontal field above the light bridges. Because these jets are not fully opaque in the wings of most chromospheric lines, it is not possible to study their spectra without highly complex considerations of radiative transfer in spectral lines from the atmosphere behind the fan.Aims. We take advantage of a unique set of observations of the Hα line along with the Ca II 8542 Å and Ca II K lines obtained with the CRISP and CHROMIS instrument of the Swedish 1-m Solar Telescope to study the physical properties of a fan-shaped jet that was backlit by an X9.3 flare. For what we believe to be the first time, we report an observationally derived estimate of the mass and density of material in a fan-shaped jet.Methods. The Hα flare ribbon emission profiles from behind the fan are highly broadened and flattened, allowing us to investigate the fan with a single slab via Beckers’ cloud model, as if it were backlit by a flat spectral profile of continuum emission. Using this model we derived the opacity and velocity of the material in the jet. Using inversions of Ca II 8542 Å emission via the STockholm inversion Code, we were also able to estimate the temperature and to cross-check the velocity of the material in the jet. Finally, we used the masses and the plane-of-sky and line-of-sight velocities as functions of time to investigate the downward supply of energy and momentum to the photosphere in the collapse of this jet, and evaluated it as a potential driver for a sunquake beneath.Results. We find that the physical properties of the fan material are reasonably chromospheric in nature, with a temperature of 7050 ± 250 K and a mean density of 2 ± 0.3 × 10−11 g cm−3.Conclusions. The total mass observed in Hα was found to be 3.9 ± 0.7 × 1013 g and the kinetic energy delivered to the base of the fan in its collapse was nearly two orders of magnitude below typical sunquake energies. We therefore rule out this jet as the sunquake driver, but cannot completely rule out larger fan jets as potential drivers.
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| 6. |
- 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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| 7. |
- Quintero Noda, C., et al.
(författare)
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The European Solar Telescope
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Télescope Héliographique pour l’Étude du Magnétisme et des Instabilités Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems.
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| 8. |
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Universum på glänt: Hundra år av svensk astronomi
- 2021
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Svenska astronomiska sällskapet firade hundra år 2019. Detta högtidlighölls bland annat genom en blogg där vi i hundra artiklar försökte skildra vad svenska astronomi är och har varit under det senaste seklet. Denna blogg har vi nu stöpt om till bokform. Samlingen visar på den snabba utvecklingen inom astronomi och rymdforskning. Därtill illustreras bredden i verksamheten med världsledande svenska forskare, idoga amatörastronomer och visionära folkbildare i viktiga roller.
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| 9. |
- van Noort, M., et al.
(författare)
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A prototype of a microlensed hyperspectral imager for solar observations
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 668
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Tidskriftsartikel (refereegranskat)abstract
- Context. When spectropolarimetric data are recorded at high spatial, spectral, and temporal resolution, the quality of the data is generally limited by the signal-to-noise ratio.Aims. We present a prototype of an integral field spectrograph for solar observations. This prototype overcomes the limitations of traditional solar instrumentation and captures the spectral information for all points in a given field of view without scanning, in order to optimize the efficiency and to minimize spectral and spatial crosstalk.Methods. The prototype was executed as a plug-in for the TRIPPEL spectrograph at the Swedish 1-meter Solar Telescope (SST) and uses an array of microlenses to shrink each image element, so that dark space is created in between. The light is then dispersed in this space, allowing for the independent detection of each spatio-spectral image element on a 2D detector.Results. The prototype was built and installed at the SST, yielding several good-quality data sets. These data sets were used to determine the imaging performance and efficiency of the prototype.Conclusions. Although the instrument required high-accuracy optics, the transparency of the prototype was found to be about 25%, and the straylight properties were found to be typical for spectrographic instruments.
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