Presentasjon av masteroppgave: Isak Aaby
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«Impact of non-instantaneous spectral imaging of the quiet Sun»
Abstract:
Fabry–Perot interferometers are frequently used in telescopes to observe the solar atmosphere because they make it possible to obtain diffraction-limited images. These instruments obtain 3D spectrograms of the Sun by acquiring several narrowband images sequentially. During the scanning process, there is a risk of information being lost because of fast-moving events occurring in the atmosphere.
We aim to investigate the consequences of this scanning time for the CRISP instrument at the Swedish 1-meter Solar Telescope using a forward-modelling approach. We want to determine how much additional information is lost by acquiring wavelengths at different times. We make use of a unique quiet-Sun 3D magnetohydrodynamic simulation from Bifrost with a very high temporal cadence of 0.1 s. Based on the simulation, we synthesized Stokes I profiles for Fe I 617.3 nm and Ca II 854.2 nm using detailed radiative transfer calculations. We then mimic the spatial and spectral resolutions of SST/CRISP, as well as the non-instantaneous wavelength acquisition time, using the instrumental profile.
Fast-moving events did occur in the provided simulation, but they were rare. Our analysis shows that the produced continuum for both lines is stable during synthetic spectral scans. Only 0.13% of spatial pixels for Fe I 617.3 nm exhibited a continuum change larger than 5% during a spectral scan. A spatial degradation of the synthetic spectra did not provide a significant change, since the spatial resolution of the simulation was already very close to the observed one. Applying spectral convolution with all wavelengths measured at the same time produces profiles with significantly weaker absorption in the line cores of Fe I 617.3 nm and Ca II 854.2 nm. Accounting for the time effect of CRISP observations does not lead to substantial degradation. During a few energetic events, a sequential wavelength acquisition failed to capture rapid emission in the line core of Ca II 854.2 nm. However, these events were rare.
This thesis demonstrates that very little information is lost by acquiring wavelengths at different times when observing Stokes I profiles for Fe I 617.3 nm and Ca II 854.2 nm in the quiet Sun. Larger time effects could instead be produced by acquiring the full Stokes vector, which would increase the total scanning time.
Image caption: The Swedish 1-m Solar Telescope right after sunrise ready to take observations. Credit: Nicolas Poirier.
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More information: https://www.mn.uio.no/astro/studier/aktuelt/arrangementer/masterpresentasjoner/2026/Isak%20Aaby.html
Abstract:
Fabry–Perot interferometers are frequently used in telescopes to observe the solar atmosphere because they make it possible to obtain diffraction-limited images. These instruments obtain 3D spectrograms of the Sun by acquiring several narrowband images sequentially. During the scanning process, there is a risk of information being lost because of fast-moving events occurring in the atmosphere.
We aim to investigate the consequences of this scanning time for the CRISP instrument at the Swedish 1-meter Solar Telescope using a forward-modelling approach. We want to determine how much additional information is lost by acquiring wavelengths at different times. We make use of a unique quiet-Sun 3D magnetohydrodynamic simulation from Bifrost with a very high temporal cadence of 0.1 s. Based on the simulation, we synthesized Stokes I profiles for Fe I 617.3 nm and Ca II 854.2 nm using detailed radiative transfer calculations. We then mimic the spatial and spectral resolutions of SST/CRISP, as well as the non-instantaneous wavelength acquisition time, using the instrumental profile.
Fast-moving events did occur in the provided simulation, but they were rare. Our analysis shows that the produced continuum for both lines is stable during synthetic spectral scans. Only 0.13% of spatial pixels for Fe I 617.3 nm exhibited a continuum change larger than 5% during a spectral scan. A spatial degradation of the synthetic spectra did not provide a significant change, since the spatial resolution of the simulation was already very close to the observed one. Applying spectral convolution with all wavelengths measured at the same time produces profiles with significantly weaker absorption in the line cores of Fe I 617.3 nm and Ca II 854.2 nm. Accounting for the time effect of CRISP observations does not lead to substantial degradation. During a few energetic events, a sequential wavelength acquisition failed to capture rapid emission in the line core of Ca II 854.2 nm. However, these events were rare.
This thesis demonstrates that very little information is lost by acquiring wavelengths at different times when observing Stokes I profiles for Fe I 617.3 nm and Ca II 854.2 nm in the quiet Sun. Larger time effects could instead be produced by acquiring the full Stokes vector, which would increase the total scanning time.
Image caption: The Swedish 1-m Solar Telescope right after sunrise ready to take observations. Credit: Nicolas Poirier.
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More information: https://www.mn.uio.no/astro/studier/aktuelt/arrangementer/masterpresentasjoner/2026/Isak%20Aaby.html
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Institute of Theoretical Astrophysics, University of Oslo, Sognsveien 77B, 0855 Oslo, Norge, Oslo, Norway
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Host or PublisherInstitute of Theoretical Astrophysics, University of Oslo
