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- 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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| 2. |
- Pietrow, Alexander G. M., 1991-, et al.
(författare)
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Solar oxygen abundance using SST/CRISP center-to-limb observations of the O I 7772 Å line
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 672
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Tidskriftsartikel (refereegranskat)abstract
- Solar oxygen abundance measurements based on the O I near-infrared triplet have been a much debated subject for several decades, since non-local thermodynamic equilibrium (NLTE) calculations with 3D radiation-hydrodynamics model atmospheres introduced a large change to the 1D LTE modeling. In this work, we aim to test solar line formation across the solar disk using new observations obtained with the SST/CRISP instrument. The observed data set is based on a spectroscopic mosaic that stretches from disk center to the solar limb. By comparing the state-of-the-art 3D NLTE models with the data, we find that the 3D NLTE models provide an excellent description of the line formation across the disk. We obtain an abundance value of A(O)=(8.73 +/- 0.03) dex, with a very small angular dispersion across the disk. We conclude that spectroscopic mosaics are excellent probes for geometric and physical properties of hydrodynamics models and NLTE line formation.
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| 3. |
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| 4. |
- Pietrow, Alexander G. M., 1991-
(författare)
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Did Christiaan Huygens need glasses? A study of Huygens' telescope equations and tables
- 2023
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Ingår i: Notes and records of the Royal Society of London. - : The Royal Society. - 0035-9149 .- 1743-0178.
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Tidskriftsartikel (refereegranskat)abstract
- In the later stages of his life, Christiaan Huygens semi-empirically derived a set of relations between the objective focus and diameter, the eyepiece focus, and the magnification that resulted from combining the two lenses. These relations were used by him and his brother to build what he believed were optimized telescopes. When comparing these equations to the ones derived from modern optical principles, Huygens' telescopes were in fact far from optimal. While there are several potential reasons for this discrepancy, one possible reason, explored in this work, is that Huygens might have suffered from a mild case of myopia (or near-sightedness) and that he compensated this condition by building telescopes that overmagnified by a factor of 3.5. Based on this hypothesis, Huygens' visual acuity is estimated to be around 20/70, which on average corresponds to an optical prescription of -1.5 diopters.
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| 5. |
- Pietrow, Alexander G.M. 1991-
(författare)
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Investigations into the origin of Einstein’s Sink
- 2018
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Ingår i: Studium. - : Uopen Journals. - 1876-9055 .- 2212-7283. ; 11:4, s. 260-268
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Tidskriftsartikel (refereegranskat)abstract
- Einstein’s sink is a well-known object among physics and astronomy students at Leiden University. Stories about its origin have been passed down since it was moved to the large lecture room of the then newly built Oort Building in 1998. These stories claim that it was seen as an Einstein relic by the physics faculty, kept close to inspire young minds. After researching this story, I found that the sink is from the early 20th century and that it once stood in the large lecture room of the Kamerlingh Onnes Laboratory in Leiden. It is likely that at this time it was used by many scientists, including Einstein. However, my research also shows that the move from the KOL was done purely for financial reasons and had nothing to do with Einstein. It is possible that the story was made up to conceal this fact, creating a more appealing reason for these cutbacks. The sink is seen by many as a connection to Einstein’s and the university’s past and is liked for this fact and not the aforementioned legend.
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| 6. |
- 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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| 7. |
- 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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