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search.filters.applied.f.access: openAccess × DDC: 530 × Type: Text × WGL Institute: AIP ×

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Now showing 1 - 10 of 80
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    Large-scale globally propagating coronal waves
    (Katlenburg-Lindau : MPS, 2015) Warmuth, Alexander
    Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the “classical” interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which “pseudo waves” are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging.
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    Die Verarbeitung des Rohdatenflusses eines Weltrauminterferometers : Schlussbericht zur Studie ; Zeitraum: 1.3.2000 - 31.12.2001
    (Potsdam : Leibniz-Institut für Astrophysik, 2002) Hirte, Sonja; Scholz, Ralf-Dieter; Schilbach, E.
    [no abstract available]
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    Mitwirkung des AIP am Betrieb des XMM-Newton Survey Science Center : Abschlussbericht ; Laufzeit: 1.1.2002 - 31.7.2008
    (Hannover : Technische Informationsbibliothek (TIB), 2008) Schwope, Axel; Lamer, Georg
    [no abstract available]
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    Destabilization of super-rotating Taylor-Couette flows by current-free helical magnetic fields
    (London : Cambridge Univ. Press, 2021) Rüdiger, G.; Schultz, M.; Hollerbach, R.
    In an earlier paper we showed that the combination of azimuthal magnetic fields and super-rotation in Taylor–Couette flows of conducting fluids can be unstable against non-axisymmetric perturbations if the magnetic Prandtl number of the fluid is Pm≠1. Here we demonstrate that the addition of a weak axial field component allows axisymmetric perturbation patterns for Pm of order unity depending on the boundary conditions. The axisymmetric modes only occur for magnetic Mach numbers (of the azimuthal field) of order unity, while higher values are necessary for the non-axisymmetric modes. The typical growth time of the instability and the characteristic time scale of the axial migration of the axisymmetric mode are long compared with the rotation period, but short compared with the magnetic diffusion time. The modes travel in the positive or negative z direction along the rotation axis depending on the sign of BϕBz. We also demonstrate that the azimuthal components of flow and field perturbations travel in phase if |Bϕ|≫|Bz|, independent of the form of the rotation law. Within a short-wave approximation for thin gaps it is also shown (in an appendix) that for ideal fluids the considered helical magnetorotational instability only exists for rotation laws with negative shear.
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    High-Resolution Arrayed-Waveguide-Gratings in Astronomy: Design and Fabrication Challenges
    (Basel : MDPI, 2017) Stoll, Andreas; Zhang, Ziyang; Haynes, Roger; Roth, Martin
    A comprehensive design of a folded-architecture arrayed-waveguide-grating (AWG)-device, targeted at applications as integrated photonic spectrographs (IPS) in near-infrared astronomy, is presented. The AWG structure is designed for the astronomical H-band (1500 nm-1800 nm) with a theoretical maximum resolving power R = 60,000 at 1630 nm. The geometry of the device is optimized for a compact structure with a footprint of 5.5 cm × 3.93 cm on SiO2 platform. To evaluate the fabrication challenges of such high-resolution AWGs, effects of random perturbations of the effective refractive index (RI) distribution in the free propagation region (FPR), as well as small variations of the array waveguide optical lengths are numerically investigated. The results of the investigation show a dramatic degradation of the point spread function (PSF) for a random effective RI distribution with variance values above ~10-4 for both the FPR and the waveguide array. Based on the results, requirements on the fabrication technology for high-resolution AWG-based spectrographs are given in the end.
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    Vorbereitende Arbeiten für die Instrumente STIX und EPT für die Sondenmission Solar Orbiter der ESA : Schlussbericht zum Vorhaben
    (Hannover : Technische Informationsbibliothek (TIB), 2010) Mann, Gottfried
    [no abstract available]
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    The dynamical evolution of planetary nebulae
    (Bristol : IOP Publ., 2016) Schönberner, Detlef
    Based on modern 1D-radiation-hydrodynamics simulations of formation and evolution of planetary nebulae, I discuss in detail the basic dynamical processes responsible for the "grand design" of most planetary nebulae, i.e. their double-shell morphology and their typical expansion properties. Special emphasis is given for a proper definition of a nebula's true expansion rate and its relation to spectroscopically measurable Doppler velocities of the expanding material. It is found that the typical nebular expansion is about twice as fast as hitherto assumed, viz. ≃45 kms-1.
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    Mitwirkung bei Aufbau und Betrieb des XMM Survey Scientist Center : Schlußbericht zum DLR Projekt 50 OX 9801 3
    (Potsdam : Leibniz-Institut für Astrophysik, 2001) Brunner, Hermann; Schwope, Axel
    [no abstract available]