1,017 research outputs found

    First Metis Detection of the Helium D3 Line Polarization in a Large Eruptive Prominence

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    Metis on board Solar Orbiter is the space coronagraph developed by an Italian-German-Czech consortium. It is capable of observing solar corona and various coronal structures in the visible-light (VL) and UV (hydrogen Lyα) channels simultaneously for the first time. Here we present observations of a large eruptive prominence on 2021 April 25-26, in the VL, taken during the mission cruise phase, and demonstrate that apart from the broadband continuum emission, which is due to the Thomson scattering on prominence electrons, we detect a significant radiation in the neutral-helium D3 line (587.6 nm), which lies within the Metis VL passband. We show how the prominence looks like in Stokes I, Q, and U. We consider two extreme cases of the prominence magnetic field, and we separate the Stokes I and Q signals pertinent to Thomson scattering and to the D3 line. The degree of linear polarization of the D3 line (both Q and U) indicates the presence of the prominence magnetic field; hence Metis can serve as a magnetograph for eruptive prominences located high in the corona

    Co-Design of a Controller and Its Digital Implementation: The MOBY-DIC2 Toolbox for Embedded Model Predictive Control

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    In this capsule, the MOBY-DIC2 Toolbox is used to design implicit/explicit/approximate Model Predictive Control (MPC) for a DC-DC buck converter, reproducing the results shown in the publication "Co-Design of a Controller and Its Digital Implementation: The MOBY-DIC2 Toolbox for Embedded Model Predictive Control". MOBY-DIC2 Toolbox is a MATLAB toolbox for the automatic generation of embedded control systems based on MPC. The main feature of the toolbox is the automatic generation of C and/or VHDL code, for the circuit implementation of controllers (either exact/approximate explicit or implicit) and observers on microcontrollers and/or Field Programmable Gate Arrays (FPGA), respectively. Also, the design of model-based state observers such as Kalman filters or Kalman predictors is included in the toolbox. Simulink models for the simulation of the whole closed-loop system (comprising controller and observer) and Xilinx System Generator models for hardware-in-the-loop simulations can be easily generated

    A high-latitude coronal mass ejection observed by a constellation of coronagraphs: Solar Orbiter/Metis, STEREO-A/COR2, and SOHO/LASCO

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    Context. A few days before the first perihelion of the Solar Orbiter nominal mission, which occurred on 2022 March 26, the Metis coronagraph on board Solar Orbiter detected a coronal mass ejection (CME) that was moving away from the far side of the Sun (with respect to Solar Orbiter) at high northern latitudes. The eruption was also seen by other spacecraft, in particular, by STEREO-A, which was in quadrature configuration with Solar Orbiter. Aims. We analyse the different views of the CME by a constellation of spacecraft with the purpose to determine the speed and acceleration of the CME, and to identify the source region of the CME. Methods. Considering the positions of various spacecraft on 2022 March 22, this CME happened to be within the field of view of STEREO-A/SECCHI, and it was visible over the limb from SOHO/LASCO. We present the results of the 3D reconstruction of the CME based on the graduated cylindrical shell model and of the identification of the possible origin of the CME using extreme-ultraviolet (EUV) observations by Solar Orbiter/EUI, STEREO-A/EUVI, and SDO/AIA. The observations in EUV are compared with the coronal magnetic structure obtained by the potential field source surface method. Results. The 3D reconstruction of the CME derives a central latitude of 29 N, a Stonyhurst longitude of 125, and an average radial speed at the apex of 322 ± 33 km s1 between 4 and 13 RÈź, which is probably not high enough to generate a shock wave. The estimated average acceleration of the CME is 16 ± 11 m s2 in the same range of distances from the Sun. This CME may be associated with the disappearance of a coronal cloud prominence, which is seen in the EUV by STEREO-A/EUVI and SDO/AIA, and is also associated with rapidly evolving emerging magnetic flux

    In-flight radiometric calibration of the Metis Visible Light channel using stars and comparison with STEREO-A/COR2 data

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    Context. We present the results for the in-flight radiometric calibration performed for the Visible Light (VL) channel of the Metis coronagraph on board Solar Orbiter. Aims. The radiometric calibration is a fundamental step in building the official pipeline of the instrument, devoted to producing the calibrated data in physical units (L2 data). Methods. To obtain the radiometric calibration factor (ĂÎŒVL), we used stellar targets transiting the Metis field of view. We derived ĂÎŒVLby determining the signal of each calibration star by means of the aperture photometry and calculating its expected flux in the Metis band pass. The analyzed data set covers the time range from the beginning of the Cruise Phase of the mission (June 2020) until March 2021. Results. Considering the uncertainties, the estimated factor ĂÎŒVLis in a good agreement with that obtained during the on-ground calibration campaign. This implies that up to March 2021 there was no measurable reduction in the VL channel throughput. Finally, we compared the total and polarized brightness visible light images of the solar corona acquired with Metis and STEREO-A/COR2 during the November 2020 superior conjunction of these instruments. A general good agreement was obtained between the images of these instruments for both the total and polarized brightness

    Three-dimensional reconstruction of type U radio bursts: a novel remote sensing approach for coronal loops

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    Type U radio bursts are impulsive coherent radio emissions produced by the Sun that indicate the presence of subrelativistic electron beams propagating along magnetic loops in the solar corona. In this work, we present the analysis of a type U radio burst that was exceptionally imaged on 2011 March 22 by the Nançay Radioheliograph (NRH) at three different frequencies (298.7, 327.0, and 360.8 MHz). Using a novel modelling approach, we show for the first time that the use of high-resolution radio heliograph images of type U radio bursts can be sufficient to both accurately reconstruct the 3D morphology of coronal loops (without recurring to triangulation techniques) and to fully constrain their physical parameters. At the same time, we can obtain unique information on the dynamics of the accelerated electron beams, which provides important clues as to the plasma mechanisms involved in their acceleration and as to why type U radio bursts are not observed as frequently as type III radio bursts. We finally present plausible explanations for a problematic aspect related to the apparent lack of association between the modeled loop as inferred from radio images and the extreme-ultraviolet (EUV) structures observed from space in the same coronal region

    A high-latitude coronal mass ejection observed by a constellation of coronagraphs: Solar Orbiter/Metis, STEREO-A/COR2, and SOHO/LASCO

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    Context. A few days before the first perihelion of the Solar Orbiter nominal mission, which occurred on 2022 March 26, the Metis coronagraph on board Solar Orbiter detected a coronal mass ejection (CME) that was moving away from the far side of the Sun (with respect to Solar Orbiter) at high northern latitudes. The eruption was also seen by other spacecraft, in particular, by STEREO-A, which was in quadrature configuration with Solar Orbiter. Aims. We analyse the different views of the CME by a constellation of spacecraft with the purpose to determine the speed and acceleration of the CME, and to identify the source region of the CME. Methods. Considering the positions of various spacecraft on 2022 March 22, this CME happened to be within the field of view of STEREO-A/SECCHI, and it was visible over the limb from SOHO/LASCO. We present the results of the 3D reconstruction of the CME based on the graduated cylindrical shell model and of the identification of the possible origin of the CME using extreme-ultraviolet (EUV) observations by Solar Orbiter/EUI, STEREO-A/EUVI, and SDO/AIA. The observations in EUV are compared with the coronal magnetic structure obtained by the potential field source surface method. Results. The 3D reconstruction of the CME derives a central latitude of 29° N, a Stonyhurst longitude of −125°, and an average radial speed at the apex of 322 ± 33 km s−1 between 4 and 13 R⊙, which is probably not high enough to generate a shock wave. The estimated average acceleration of the CME is 16 ± 11 m s−2 in the same range of distances from the Sun. This CME may be associated with the disappearance of a coronal cloud prominence, which is seen in the EUV by STEREO-A/EUVI and SDO/AIA, and is also associated with rapidly evolving emerging magnetic flux

    Theoretical, on-ground, and in-flight study of the Metis coronagraph vignetting

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    On-board the Solar Orbiter ESA/NASA mission there is Metis, a coronagraph designed to study the solar corona by providing an artificial solar eclipse. Metis features two channels working at the ultraviolet Lyman-α (121.6 nm) and in the visible light (580-640 nm). On-ground, the Metis radiometric performance has been tested using a flat-field panel (uniform illumination); the stability of the performance can be verified in-flight through the analysis of the stars passing in the Metis Field of View. Care must be taken to ensure the quality of the calibration, both before launch and for the long period associated with the space mission lifetime. For this reason, we are carrying out long period research of stars that cross the Field of View of Metis. In this paper, we describe the vignetting function acquired: on-ground, simulated via a raytracing code and in-flight derived from on-ground measurements (performing some adjustments to account for the real Metis flight configuration). These vignetting functions are then compared with the vignetting data derived from the passage of the star Theta Ophiuchi in March and December 2021. Additional presentation content can be accessed on the supplemental content page

    In-flight radiometric calibration of the Metis Visible Light channel using stars and comparison with STEREO-A/COR2 data

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    Context. We present the results for the in-flight radiometric calibration performed for the Visible Light (VL) channel of the Metis coronagraph on board Solar Orbiter. Aims. The radiometric calibration is a fundamental step in building the official pipeline of the instrument, devoted to producing the calibrated data in physical units (L2 data). Methods. To obtain the radiometric calibration factor (ϔVL), we used stellar targets transiting the Metis field of view. We derived ϔVLby determining the signal of each calibration star by means of the aperture photometry and calculating its expected flux in the Metis band pass. The analyzed data set covers the time range from the beginning of the Cruise Phase of the mission (June 2020) until March 2021. Results. Considering the uncertainties, the estimated factor ϔVLis in a good agreement with that obtained during the on-ground calibration campaign. This implies that up to March 2021 there was no measurable reduction in the VL channel throughput. Finally, we compared the total and polarized brightness visible light images of the solar corona acquired with Metis and STEREO-A/COR2 during the November 2020 superior conjunction of these instruments. A general good agreement was obtained between the images of these instruments for both the total and polarized brightness

    Coronal mass ejection followed by a prominence eruption and a plasma blob as observed by Solar Orbiter

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    Context. On 2021 February 12, two subsequent eruptions occurred above the western limb of the Sun, as seen along the Sun-Earth line. The first event was a typical slow coronal mass ejection (CME), followed ∌7 h later by a smaller and collimated prominence eruption, originating south of the CME, followed by a plasma blob. These events were observed not only by the SOHO and STEREOA missions, but also by the suite of remote-sensing instruments on board Solar Orbiter. Aims. We show how data acquired by the Full Sun Imager (FSI), the Metis coronagraph, and the Heliospheric Imager (HI) from the Solar Orbiter perspective can be combined to study the eruptions and different source regions. Moreover, we show how Metis data can be analyzed to provide new information about solar eruptions. Methods. Different 3D reconstruction methods were applied to the data acquired by different spacecraft, including remote-sensing instruments on board Solar Orbiter. Images acquired by the two Metis channels in the visible light (VL) and Hi Ly-α line (UV) were combined to derive physical information about the expanding plasma. The polarization ratio technique was also applied for the first time to Metis images acquired in the VL channel. Results. The two eruptions were followed in 3D from their source region to their expansion in the intermediate corona. By combining VL and UV Metis data, the formation of a post-CME current sheet (CS) was followed for the first time in the intermediate corona. The plasma temperature gradient across a post-CME blob propagating along the CS was also measured for the first time. Application of the polarization ratio technique to Metis data shows that by combining four different polarization measurements, the errors are reduced by ∌5-7%. This constrains the 3D plasma distribution better

    Connecting Solar Orbiter remote-sensing observations and Parker Solar Probe in situ measurements with a numerical MHD reconstruction of the Parker spiral

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    As a key feature, NASA’s Parker Solar Probe (PSP) and ESA-NASA’s Solar Orbiter (SO) missions cooperate to trace solar wind and transients from their sources on the Sun to the inner interplanetary space. The goal of this work is to accurately reconstruct the interplanetary Parker spiral and the connection between coronal features observed remotely by the Metis coronagraph on-board SO and those detected in situ by PSP at the time of the first PSP-SO quadrature of January 2021. We use the Reverse in situ and MHD Approach (RIMAP), a hybrid analytical-numerical method performing data-driven reconstructions of the Parker spiral. RIMAP solves the MHD equations on the equatorial plane with the PLUTO code, using the measurements collected by PSP between 0.1 and 0.2 AU as boundary conditions. Our reconstruction connects density and wind speed measurements provided by Metis (3–6 solar radii) to those acquired by PSP (21.5 solar radii) along a single streamline. The capability of our MHD model to connect the inner corona observed by Metis and the super Alfvénic wind measured by PSP, not only confirms the research pathways provided by multi-spacecraft observations, but also the validity and accuracy of RIMAP reconstructions as a possible test bench to verify models of transient phenomena propagating across the heliosphere, such as coronal mass ejections, solar energetic particles and solar wind switchbacks
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