Influence of misalignments on performance of externally occulted solar coronagraphs. Application to PROBA-3/ASPIICS

ASPIICS is a novel externally occulted coronagraph that will be launched onboard the PROBA-3 mission of ESA. The external occulter (EO) will be placed on one satellite ~150 m ahead of the second satellite with an optical instrument. During part of each orbit, the satellites will fly in a precise formation, constituting a giant externally occulted coronagraph. Large distance between the EO and the primary objective will allow observations of the white-light solar corona starting already from ~1.1RSun. We analyze influence of shifts of the satellites and misalignments of optical elements on diffracted light. Based on the quantitative influence of misalignments on diffracted light, we will provide a "recipe" for choosing the size of the internal occulter (IO) to achieve a trade-off between the minimal height of observations and sustainability to possible misalignments. We implement a numerical model of the diffracted light and its propagation through the optical system, and compute intensities of diffracted light throughout the instrument. Our numerical model extends axi-symmetrical model of Rougeot et al. 2017 to non-symmetrical cases. The computations fully confirm main properties of the diffracted light obtained from semi-analytical consideration. Results: relative influences of various misalignments are significantly different. We show that: the IO with R=1.1RSun is large enough to compensate possible misalignments in ASPIICS, apodizing the edge of the IO leads to additional suppression of the diffracted light. Conclusions: the most important misalignment is the tilt of the telescope WRT the line connecting the center of the EO and the entrance aperture. Special care should be taken to co-align the EO and the coronagraph, i.e. co-aligning the diffraction fringe from the EO and the IO. We suggest that the best orientation strategy is to point the coronagraph to the center of the EO.Comment: 13 pages, 15 figure

Modeling and removal of optical ghosts in the PROBA-3/ASPIICS externally occulted solar coronagraph

Context: ASPIICS is a novel externally occulted solar coronagraph, which will be launched onboard the PROBA-3 mission of the European Space Agency. The external occulter will be placed on the first satellite approximately 150 m ahead of the second satellite that will carry an optical instrument. During 6 hours per orbit, the satellites will fly in a precise formation, constituting a giant externally occulted coronagraph. Large distance between the external occulter and the primary objective will allow observations of the white-light solar corona starting from extremely low heights 1.1RSun. Aims: To analyze influence of optical ghost images formed inside the telescope and develop an algorithm for their removal. Methods: We implement the optical layout of ASPIICS in Zemax and study the ghost behaviour in sequential and non-sequential regimes. We identify sources of the ghost contributions and analyze their geometrical behaviour. Finally we develop a mathematical model and software to calculate ghost images for any given input image. Results: We show that ghost light can be important in the outer part of the field of view, where the coronal signal is weak, since the energy of bright inner corona is redistributed to the outer corona. However the model allows to remove the ghost contribution. Due to a large distance between the external occulter and the primary objective, the primary objective does not produce a significant ghost. The use of the Lyot spot in ASPIICS is not necessary.Comment: 14 pages, 13 figure

Nonlinear evolution of short-wavelength torsional Alfvén waves

We analyze nonlinear evolution of torsional Alfvén waves in a straight magnetic flux tube filled in with a low-β plasma, and surrounded with a plasma of lower density. Such magnetic tubes model, in particular, a segment of a coronal loop or a polar plume. The wavelength is taken comparable to the tube radius. We perform a numerical simulation of the wave propagation using ideal magnetohydrodynamics. We find that a torsional wave nonlinearly induces three kinds of compressive flows: the parallel flow at the Alfvén speed, which constitutes a bulk plasma motion along the magnetic field, the tube wave, and also transverse flows in the radial direction, associated with sausage fast magnetoacoustic modes. In addition, the nonlinear torsional wave steepens and its propagation speed increases. The latter effect leads to the progressive distortion of the torsional wave front, i.e., nonlinear phase mixing. Because of the intrinsic non-uniformity of the torsional wave amplitude across the tube radius, the nonlinear effects are more pronounced in regions with higher wave amplitudes. They are always absent at the axes of the flux tube. In the case of a linear radial profile of the wave amplitude, the nonlinear effects are localized in an annulus region near the tube boundary. Thus, the parallel compressive flows driven by torsional Alfvén waves in the solar and stellar coronae, are essentially non-uniform in the perpendicular direction. The presence of additional sinks for the wave energy reduces the efficiency of the nonlinear parallel cascade in torsional Alfvén waves

Short-Period Internal Waves under an Ice Cover in Van Mijen Fjord, Svalbard

Temperature and velocity fluctuations measured in Van Mijen Fjord in Svalbard and interpreted as the fluctuations induced by internal waves revealed the existence of short-period internal waves with an amplitude of approximately 1 m and a period of approximately 5–10 min that correlate with the ice cover fluctuations of the same period with an amplitude of a few millimeters

LUCI onboard Lagrange, the Next Generation of EUV Space Weather Monitoring

LUCI (Lagrange eUv Coronal Imager) is a solar imager in the Extreme UltraViolet (EUV) that is being developed as part of the Lagrange mission, a mission designed to be positioned at the L5 Lagrangian point to monitor space weather from its source on the Sun, through the heliosphere, to the Earth. LUCI will use an off-axis two mirror design equipped with an EUV enhanced active pixel sensor. This type of detector has advantages that promise to be very beneficial for monitoring the source of space weather in the EUV. LUCI will also have a novel off-axis wide field-of-view, designed to observe the solar disk, the lower corona, and the extended solar atmosphere close to the Sun-Earth line. LUCI will provide solar coronal images at a 2-3 minute cadence in a pass-band centred on 19.5 nm. Observations made through this pass-band allow for the detection and monitoring of semi-static coronal structures such as coronal holes, prominences, and active regions; as well as transient phenomena such as solar flares, limb Coronal Mass Ejections (CMEs), EUV waves, and coronal dimmings. The LUCI data will complement EUV solar observations provided by instruments located along the Sun-Earth line such as PROBA2-SWAP, SUVI-GOES and SDO-AIA, as well as provide unique observations to improve space weather forecasts. Together with a suite of other remote-sensing and in-situ instruments onboard Lagrange, LUCI will provide science quality operational observations for space weather monitoring

ОСОБЕННОСТИ КЛИНИЧЕСКОГО ТЕЧЕНИЯ АНТИ-N-МЕТИЛ-D-АСПАРТАТ РЕЦЕПТОРНОГО ЭНЦЕФАЛИТА (СЛУЧАИ ИЗ ПРАКТИКИ)

The article describes the clinical cases of anti-N-methylD-aspartate receptor encephalitis of two patients. An analysis of the dynamics of neurologic symptoms, the results of neurovisualization and neurophysiological examinations was carried out. It was shown that in patients with AntiN-methyl-D-aspartate receptor encephalitis, neurological symptoms are similar in their manifestations with symptoms of virus encephalitis. At the same time, the mechanism of development and etiology of this form of autoimmune pathology is not understood. Also, no pathognomonic changes were detected for MRI of the brain, PET, EEG for Anti-N-methylD-aspartate receptor encephalitis. The authors conclude that the diversity of neurological symptoms in patients with antiN-methyl-D-aspartate receptor encephalitis may be due not only to dysfunction of brain structures due to disruption of NMDA receptor activity, but also to a reversible disruption of functional interrelationships between different parts of the brain. В статье приводится описание клинического течения Анти-N-метил-D-аспарт рецепторного энцефалита у двух пациенток. Проведен анализ динамики неврологической симптоматики, результатов нейровизуализационных и нейрофизиологических обследований. Показано, что у пациентов с Анти-N-метил-D-аспартат рецепторным энцефалитом неврологическая симптоматика схожа по своим проявлениям с симптоматикой при инфекционных энцефалитах. В то же время механизм развития и этиология данной формы аутоиммунной патологии до конца не ясны. Также не выявлено патогномоничных только для Анти-N-метил-D-аспартат рецепторного энцефалита изменений на МРТ головного мозга, ПЭТ, ЭЭГ. Авторы делают вывод, что разнообразие неврологической симптоматики у пациентов с Анти-N-метил-D-аспартат рецепторным энцефалитом может быть обусловлено не только дисфункцией структур мозга в результате нарушения активности NMDA рецепторов, но и обратимым нарушением функциональных взаимосвязей между различными отделами мозга.