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Subject: Corona ×

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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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    The STIX Aspect System (SAS): The Optical Aspect System of the Spectrometer/Telescope for Imaging X-Rays (STIX) on Solar Orbiter
    (Dordrecht [u.a.] : Springer Science + Business Media B.V, 2020) Warmuth, A.; Önel, H.; Mann, G.; Rendtel, J.; Strassmeier, K.G.; Denker, C.; Hurford, G.J.; Krucker, S.; Anderson, J.; Bauer, S.-M.; Bittner, W.; Dionies, F.; Paschke, J.; Plüschke, D.; Sablowski, D.P.; Schuller, F.; Senthamizh Pavai, V.; Woche, M.; Casadei, D.; Kögl, S.; Arnold, N.G.; Gröbelbauer, H.-P.; Schori, D.; Wiehl, H.J.; Csillaghy, A.; Grimm, O.; Orleanski, P.; Skup, K.R.; Bujwan, W.; Rutkowski, K.; Ber, K.
    The Spectrometer/Telescope for Imaging X-rays (STIX) is a remote sensing instrument on Solar Orbiter that observes the hard X-ray bremsstrahlung emission of solar flares. This paper describes the STIX Aspect System (SAS), a subunit that measures the pointing of STIX relative to the Sun with a precision of ±4′′, which is required to accurately localize the reconstructed X-ray images on the Sun. The operating principle of the SAS is based on an optical lens that images the Sun onto a plate that is perforated by small apertures arranged in a cross-shaped configuration of four radial arms. The light passing through the apertures of each arm is detected by a photodiode. Variations of spacecraft pointing and of distance from the Sun cause the solar image to move over different apertures, leading to a modulation of the measured lightcurves. These signals are used by ground analysis to calculate the locations of the solar limb, and hence the pointing of the telescope.