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(Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2019)The evolution of the virial overdensity Δvir for ΛCDM and seven dynamical dark-energy models is investigated in the extended spherical collapse model (SCM). Here the virialization process is naturally achieved by introducing ...
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(Master thesis / Masteroppgave, 2013)Modified gravity theories are a popular research field in the hope that they could explain some of the unanswered questions in cosmology, for example how the universe starts, evolves and ends. One way to test proposed ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)Screened modified gravity predicts potentially large signatures in the peculiar velocity field that makes it an interesting probe to test gravity on cosmological scales. We investigate the signatures induced by the Symmetron ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2023)Recent studies have identified the potential for coronal wave heating to balance radiative losses in a transversely oscillating low-density loop undergoing resonant absorption, phase mixing and the Kelvin–Helmholtz ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2013)The heating of the Sun's chromosphere remains poorly understood. While progress has been made on understanding what drives the quiet-Sun internetwork chromosphere, chromospheric heating in strong magnetic field regions ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)We use coordinated observations with the Interface Region Imaging Spectrograph (IRIS) and the Swedish 1 m Solar Telescope to identify the disk counterpart of type II spicules in upper-chromospheric and transition region ...
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(Master thesis / Masteroppgave, 2010)
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2019)We studied the physical parameters of the penumbra in a large and fully developed sunspot, one of the largest over the last two solar cycles, by using full-Stokes measurements taken at the photospheric Fe i 617.3 nm and ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2023)We present a new 3D magnetohydrodynamic (MHD) heliospheric model for space-weather forecasting driven by boundary conditions defined from white-light observations of the solar corona. The model is based on the MHD code ...
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(Doctoral thesis / Doktoravhandling, 2007)Doktorgradsavhandlingen beskriver et programvarebibliotek utviklet av Øystein Olsen ved Institutt for teoretisk astrofysikk. Programvaren har blitt brukt til å finne regioner med stabile og ustabile baner rundt asteroider ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2019)We present high-resolution, high-cadence observations of six, fine-scale, on-disk jet-like events observed by the High-resolution Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We combine the Hi-C 2.1 ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2021)Abstract Since the very beginning of astronomy the location of objects on the sky has been a fundamental observational quantity that has been taken for granted. While precise two dimensional positional information is easy ...
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(Master thesis / Masteroppgave, 2011)Spicules are relatively small, narrow and elongated structures that stick out above the edge of the solar disk. They are very dynamic and appear as jets that shoot out into the outer solar atmosphere. Up until recently, ...
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(Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2020)We report detection of oscillations in brightness temperature, size and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2022)Using high-cadence observations from the Hydrogen-alpha Rapid Dynamics camera imaging system on the Dunn Solar Telescope, we present an investigation of the statistical properties of transverse oscillations in spicules ...
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(Master thesis / Masteroppgave, 2021)The CO Mapping Array Pathfinder (COMAP) is an intensity mapping experiment targeting the emission from rotational lines of carbon monoxide, redshifted to the frequency range of 26-34 GHz. In this first phase of a planned ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2016)Aims. We present a ground-based, near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z = 0.18, which is one of the most powerful gravitational telescopes that nature provides. Methods. Our ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2023)Abstract High-resolution spectral observations of the lower solar atmosphere (chromosphere and transition region) during coronal heating events, in combination with predictions from models of impulsively heated ...
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(Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2014)We present the first results of sunspot oscillations from observations by the Interface Region Imaging Spectrograph. The strongly nonlinear oscillation is identified in both the slit-jaw images and the spectra of several ...