Browsing Institutt for teoretisk astrofysikk by Title

Now showing items 499-518 of 518

  • Transverse Oscillations in Slender Ca II H Fibrils Observed with Sunrise/SuFI 
    Jafarzadeh, Shahin; Solanki, S. K.; Gafeira, Ricardo; van Noort, M.; Barthol, P.; Blanco Rodriguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L; Hirzberger, J.; Knölker, M.; Orozco Suarez, D.; Riethmüller, T. L.; Schmidt, W. (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)
    We present observations of transverse oscillations in slender Ca ii H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high- (spatial and temporal-) resolution seeing-free observations in ...
  • Transverse Wave Induced Kelvin-Helmholtz Rolls in Spicules 
    Antolin, Patrick; Schmit, D.; Pereira, Tiago Mendes Domingos; De Pontieu, Bart Walter; De Moortel, I. (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2018)
    In addition to their jet-like dynamic behavior, spicules usually exhibit strong transverse speeds, multi-stranded structure, and heating from chromospheric to transition region temperatures. In this work we first analyze ...
  • Two-dimensional Radiative Magnetohydrodynamic Simulations of Partial Ionization in the Chromosphere. II. Dynamics and Energetics of the Low Solar Atmosphere 
    Martinez-Sykora, Juan; De Pontieu, Bart Walter; Carlsson, Mats; Hansteen, Viggo; Nobrega-Siverio, Daniel; Gudiksen, Boris Vilhelm (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)
    We investigate the effects of interactions between ions and neutrals on the chromosphere and overlying corona using 2.5D radiative MHD simulations with the Bifrost code. We have extended the code capabilities implementing ...
  • A UNIFIED COMPUTATIONAL MODEL for SOLAR and STELLAR FLARES 
    Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)
    We present a unified computational framework that can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is ...
  • Unified description of screened modified gravity 
    Brax, P; Davis, A.-C.; Li, Baojiu; Winther, Hans Arnold (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2012)
    We consider modified gravity models driven by a scalar field whose effects are screened in high density regions due to the presence of nonlinearities in its interaction potential and/or its coupling to matter. Our approach ...
  • Unifying static analysis of gravitational structures with a scale-dependent scalar field gravity as an alternative to dark matter 
    Salzano, Vincenzo; Mota, David; Capoziello, S.; Napolitano, N. R. (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2014)
    Aims: We investigated the gravitational effects of a scalar field within scalar-tensor gravity as an alternative to dark matter. Motivated by chameleon, symmetron, and f(R)-gravity models, we studied a phenomenological ...
  • Universal predictions of screened modified gravity on cluster scales 
    Gronke, Max Balthasar; Mota, David; Winther, Hans Arnold (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)
    Modified gravity models require a screening mechanism to be able to evade the stringent constraints from local gravity experiments and, at the same time, give rise to observable astrophysical and cosmological signatures. ...
  • The Universe Is Reionizing at z ~ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies 
    Mason, Charlotte A.; Treu, Tommaso; Dijkstra, Mark; Mesinger, Andrei; Trenti, Michele; Pentericci, Laura; De Barros, Stephane; Vanzella, Eros (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2018)
    We present a new flexible Bayesian framework for directly inferring the fraction of neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR, z ~ 6–10) from detections and non-detections of ...
  • Unlocking the Full Potential of Extragalactic Lyα through Its Polarization Properties 
    Eide, Marius Berge; Gronke, Max Balthasar; Dijkstra, Mark; Hayes, Matthew (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2018)
    Lyα is a powerful astrophysical probe. Not only is it ubiquitous at high redshifts, it is also a resonant line, making Lyα photons scatter. This scattering process depends on the physical conditions of the gas through which ...
  • Unresolved Fine-Scale Structure in Solar Coronal Loop-Tops 
    Scullion, Eamon; Rouppe, Van Der Voort Luc; Wedemeyer-Böhm, Sven; Antolin, Patrick (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2014)
    New and advanced space-based observing facilities continue to lower the resolution limit and detect solar coronal loops in greater detail. We continue to discover even finer substructures within coronal loop cross-sections, ...
  • Using needlets to estimate the power spectrum 
    Ingebrigtsen, Tony Asle (Master thesis / Masteroppgave, 2010)
    The statistical analysis of the Cosmic Microwave Background radiation to make estimates of the Power Spectrum is a comutationally heavy operation, involving large covariance matrices. In this thesis I explore the possibility ...
  • Using voids to unscreen modified gravity 
    Falck, Bridget Lynn; Koyama, Kazuya; Zhao, Gong-Bo; Cautun, Marius (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2018)
    The Vainshtein mechanism, present in many models of gravity, is very effective at screening dark matter haloes such that the fifth force is negligible and general relativity is recovered within their Vainshtein radii. ...
  • VLT/X-Shooter spectroscopy of the afterglow of the Swift GRB 130606A: Chemical abundances and reionisation at z ~ 6 
    Hartoog, O. E.; Malesani, D; Fynbo, J.P.U.; Goto, T; Krühler, T.; Vreeswijk, P. M.; De Cia, A.; Xu, D.; Møller, P.; Covino, S; D'Elia, V; Flores, H; Goldoni, P.; Hjorth, Jens; Jakobsson, P.; Krogager, J.-K.; Kaper, L.; Ledoux, C.; Levan, A. J.; Milvang-Jensen, B; Sollerman, J.; Sparre, M.; Tagliaferri, G; Tanvir, N. R.; de Ugarte Postigo, A.; Vergani, S. D.; Wiersema, K; Datson, J.; Salinas, R; Mikkelsen, Kristin; Aghanim, N. (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)
    Context: The reionisation of the Universe is a process that is thought to have ended around z ~ 6, as inferred from spectroscopy of distant bright background sources, such as quasars (QSO) and gamma-ray burst (GRB) afterglows. ...
  • Vortex flows in the solar chromosphere: I. Automatic detection method 
    Kato, Yoshiaki; Wedemeyer, Sven (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)
    Solar “magnetic tornadoes” are produced by rotating magnetic field structures that extend from the upper convection zone and the photosphere to the corona of the Sun. Recent studies show that these kinds of rotating features ...
  • A weak lensing analysis of the PLCK G100.2-30.4 cluster 
    Radovich, M.; Formicola, I.; Meneghetti, M.; Bartalucci, I.; Bourdin, H.; Mazzotta, P.; Moscardini, L.; Ettori, S.; Arnaud, M.; Pratt, G. W.; Aghanim, N.; Dahle, Håkon; Douspis, M.; Pointecouteau, E.; Grado, A. (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)
    We present a mass estimate of the Planck-discovered cluster PLCK G100.2-30.4, derived from a weak lensing analysis of deep Subaru griz images. We perform a careful selection of the background galaxies using the multi-band ...
  • What Causes the High Apparent Speeds in Chromospheric and Transition Region Spicules on the Sun? 
    De Pontieu, Bart Walter; Martinez-Sykora, Juan; Chintzoglou, Georgios (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)
    Spicules are the most ubuiquitous type of jets in the solar atmosphere. The advent of high-resolution imaging and spectroscopy from the Interface Region Imaging Spectrograph (IRIS) and ground-based observatories has revealed ...
  • WHAT DO IRIS OBSERVATIONS of Mg II k TELL US ABOUT THE SOLAR PLAGE CHROMOSPHERE? 
    Carlsson, Mats; Leenaarts, Jorrit; De Pontieu, Bart Walter (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)
    We analyze observations from the Interface Region Imaging Spectrograph of the Mg ii k line, the Mg ii UV subordinate lines, and the O i 135.6 $\mathrm{nm}$ line to better understand the solar plage chromosphere. We also ...
  • Why is non-thermal line broadening of spectral lines in the lower transition region of the sun independent of spatial resolution? 
    De Pontieu, Bart Walter; McIntosh, Scott; Martinez-Sykora, Juan; Peter, Hardi; Mendes Domingos Pereira, Tiago (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2015)
    Spectral observations of the solar transition region (TR) and corona show broadening of spectral lines beyond what is expected from thermal and instrumental broadening. The remaining non-thermal broadening is significant ...
  • Why is the Sun's corona so hot? Why are prominences so cool? 
    Zirker, Jack B.; Engvold, Oddbjørn (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2017)
    © 2017 American Institute of Physics.
  • Wormholes supported by hybrid metric-Palatini gravity 
    Capozziello, S.; Harko, T.; Koivisto, Tomi Sebastian; Lobo, F. S. N.; Olmo, G. J. (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2012)
    Recently, a modified theory of gravity was presented, which consists of the superposition of the metric Einstein-Hilbert Lagrangian with an f(R) term constructed à la Palatini. The theory possesses extremely interesting ...