arXiv subjects

Felix Bettonvil

Publications and source records attributed to Felix Bettonvil.

12 recordsLinked to original sources

arXiv2026

First high-contrast results on THD2 testbed after infrastructure upgrade

We present the first scientific results delivered by the upgraded THD2 high-contrast imaging testbed. We report two advances enabled by its improved stability and broadband performance. First, for the Roman Space Telescope, we demonstrate that Gaussian-shaped diversity probes outperform the baseline sinc probes by reducing non-linearities, supporting higher probe amplitudes, and improving electric field estimation efficiency. These results have led to their prioritization as an enhanced early observation for Roman. Second, within ESA's SUPPPPRESS project, we test new polarization-independent Vector Vortex Coronagraphs and design them to high-contrast performance approaching 1e-10 over a 20% bandwidth. We assess their behavior in narrow- and broadband light with active focal-plane wavefront control. Together, these results show how THD2 strengthens Europe's capability in high-contrast imaging, providing a unique platform reaching contrasts of 1e-8 to 1e-9 for developing next-generation coronagraphic technologies.

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arXiv2026

METIS for ELT: optical alignment and testing of the IFU of the LM-band spectrometer

The METIS LMS (LM-band Spectrometer) is a high-resolution (R>100,000) mid-infrared integral field spectrometer for the ESO ELT. The instrument provides the capability to measure instantaneous spectra across a 0.577 x 0.897 arcsecond field-of-view with a spatial sampling of 8.2-9.1 mas using an image slicing IFU. This paper presents the optical testing and alignment performed for the IFU sub-system. This includes the detailed characterisation of the image slicing mirror array measured via: a re-imaging test in which the slicer is positioned to re-image a point source to form 28 images due to the different tilts of the 28 slicer mirrors; and precise interferometric measurements of each of the image slicer mirrors. The paper will also give an overview of the optical alignment strategy employed during the IFU AIT process in order to reach the tight alignment requirements.

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arXiv2026

SUPPPPRESS: Prototyping and testing liquid-crystal vector vortex coronagraphs with reduced polarization leakage

The vortex coronagraph is one of the most promising candidates for the Habitable Worlds Observatory (HWO) due to its excellent theoretical performance for an off-axis telescope. A practical realization can be achieved using liquid-crystal polymers to form a vector vortex coronagraph (VVC). Reaching the $10^{-10}$ contrast required for Earth-like planet detection is, however, limited by polarization leakage caused by wavelength-dependent deviations from half-wave retardance. This effect can be mitigated using multi-layer twisted retarders to minimize leakage, and by combining the VVC with multiple polarization gratings (mgVVC) to diffract the polarization leakage out of the science path. We present recent progress within the ESA-funded SUPPPPRESS project, which aims to advance the manufacturing, assembly, and testing of high-performance VVCs. Central singularities of 2 and 6 $μ$m have been achieved for charge 2 and charge 6 VVCs, respectively, with patterning accuracies better than 1 degree root-mean-square error. Fabrication procedures have been developed to produce individual components with a polarization leakage of $3\times10^{-4}$ over a 10% bandwidth and $8\times10^{-4}$ over a 20% bandwidth. We also report on the development of assembly and alignment procedures for mgVVCs and their metrology. Furthermore, we present initial high-contrast tests at the THD2 bench for both regular VVCs and a double-grating VVC. The double-grating VVC reaches an average contrast between 3 and 10 $λ$/D of $2 \times 10^{-8}$ over a small bandwidth and $6\times 10^{-8}$ over a 10% bandwidth. Finally, we report on successful space-environment tests of the assembled liquid-crystal masks.

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arXiv2024

Prototyping liquid-crystal coronagraphs for exo-Earth imaging

This paper presents initial results from the ESA-funded ``SUPPPPRESS'' project, which aims to develop high-performance liquid-crystal coronagraphs for direct imaging of Earth-like exoplanets in reflected light. The project focuses on addressing the significant challenge of polarization leakage in vector vortex coronagraphs (VVCs). We utilize newly manufactured multi-grating, liquid-crystal VVCs, consisting of a two- or three-element stack of vortex and grating patterns, to reduce this leakage to the $10^{-10}$ contrast level. We detail the experimental setups, including calibration techniques with polarization microscopes and Mueller matrix ellipsometers to enhance the direct-write accuracy of the liquid-crystal patterns. The performance testing of these coronagraph masks will be conducted on the THD2 high-contrast imaging testbed in Paris.

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arXiv2024

METIS high-contrast imaging: from final design to manufacturing and testing

The Mid-infrared ELT Imager and Spectrograph (METIS) is one of the first-generation scientific instruments for the ELT, built under the supervision of ESO by a consortium of research institutes across and beyond Europe. Designed to cover the 3 to 13 $μ$m wavelength range, METIS had its final design reviewed in Fall 2022, and has then entered in earnest its manufacture, assembly, integration, and test (MAIT) phase. Here, we present the final design of the METIS high-contrast imaging (HCI) modes. We detail the implementation of the two main coronagraphic solutions selected for METIS, namely the vortex coronagraph and the apodizing phase plate, including their combination with the high-resolution integral field spectrograph of METIS, and briefly describe their respective backup plans (Lyot coronagraph and shaped pupil plate). We then describe the status of the MAIT phase for HCI modes, including a review of the final design of individual components such as the vortex phase masks, the grayscale ring apodizer, and the apodizing phase plates, as well as a description of their on-going performance tests and of our plans for system-level integration and tests. Using end-to-end simulations, we predict the performance that will be reached on sky by the METIS HCI modes in presence of various environmental and instrumental disturbances, including non-common path aberrations and water vapor seeing, and discuss our strategy to mitigate these various effects. We finally illustrate with mock observations and data processing that METIS should be capable of directly imaging temperate rocky planets around the nearest stars.

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arXiv2022

The dusty heart of Circinus: I. Imaging the circumnuclear dust in N-band

Active galactic nuclei play a key role in the evolution of galaxies, but their inner workings and physical connection to the host are poorly understood due to a lack of angular resolution. Infrared interferometry makes it possible to resolve the circumnuclear dust in the nearby Seyfert 2 galaxy, Circinus. Previous observations have revealed complex structures and polar dust emission but interpretation was limited to simple models. MATISSE makes it possible to image these structures for the first time. We observed the Circinus Galaxy with VLTI/MATISSE, producing 150 correlated flux spectra and 100 closure phase spectra. We reconstructed images in the N-band at ~10 mas resolution. We fit blackbody functions with dust extinction to several aperture-extracted fluxes from the images to produce a temperature distribution of central dusty structures. We find significant substructure in the circumnuclear dust: central unresolved flux of ~0.5 Jy, a thin disk 1.9 pc in diameter oriented along ~45 deg,and a ~4x1.5 pc polar emission extending orthogonal to the disk. The polar emission exhibits patchiness, which we attribute to clumpy dust. Flux enhancements to the east and west of the disk are seen for the first time. We distinguish the temperature profiles of the disk and of the polar emission: the disk shows a steep temperature gradient indicative of denser material; the polar profile is flatter, indicating clumpiness and/or lower dust density. The unresolved flux is fitted with a high temperature, ~370 K. The polar dust remains warm (~200 K) out to 1.5 pc from the disk. The recovered morphology and temperature distribution resembles modeling of accretion disks with radiation-driven winds at large scales, but we placed new constraints on the subparsec dust. The subparsec features imaged here place new constraints on the physical modeling of circumnuclear dust in active galaxies.

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arXiv2021

Thermal imaging of dust hiding the black hole in the Active Galaxy NGC 1068

In the widely accepted 'Unified Model' solution of the classification puzzle of Active Galactic Nuclei, the orientation of a dusty accretion torus around the central black hole dominates their appearance. In 'type-1' systems, the bright nucleus is visible at the centre of a face-on torus. In 'type-2' systems the thick, nearly edge-on torus hides the central engine. Later studies suggested evolutionary effects and added dusty clumps and polar winds but left the basic picture intact. However, recent high-resolution images of the archetypal type-2 galaxy NGC 1068 suggested a more radical revision. They displayed a ring-like emission feature which the authors advocated to be hot dust surrounding the black hole at the radius where the radiation from the central engine evaporates the dust. That ring is too thin and too far tilted from edge-on to hide the central engine, and ad hoc foreground extinction is needed to explain the type-2 classification. These images quickly generated reinterpretations of the type 1-2 dichotomy. Here we present new multi-band mid-infrared images of NGC1068 that detail the dust temperature distribution and reaffirm the original model. Combined with radio data, our maps locate the central engine below the previously reported ring and obscured by a thick, nearly edge-on disk, as predicted by the Unified Model. We also identify emission from polar flows and absorbing dust that is mineralogically distinct from that towards the Milky Way centre.

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arXiv2021

Simultaneous broadband radio and optical emission of meteor trains imaged by LOFAR / AARTFAAC and CAMS

We report on simultaneous 30 - 60 MHz LOFAR / AARTFAAC12 radio observations and CAMS low-light video observations of +4 to -10 magnitude meteors at the peak of the Perseid meteor shower on August 12/13, 2020. 204 meteor trains were imaged in both the radio and optical domain. Aside from scattered artificial radio sources, we identify broadband radio emission from many persistent trains, one of which lingered for up to 6 minutes. Unexpectedly, fewer broadband radio meteor trains were recorded when the experiment was repeated during the 2020 Geminids and 2021 Quadrantids. Intrinsic broadband radio emission was reported earlier by the Long Wavelength Array, but for much brighter meteors and observed with lower spatial resolution. The new results offer insight into the unknown radio emission mechanism.

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arXiv2021

METIS: The Mid-infrared ELT Imager and Spectrograph

The Mid-infrared ELT Imager and Spectrograph (METIS) will provide the Extremely Large Telescope (ELT) with a unique window to the thermal- and mid-infrared (3 - 13 microns). Its single-conjugate adaptive optics (SCAO) system will enable high contrast imaging and integral field unit (IFU) spectroscopy (R~100,000) at the diffraction limit of the ELT. This article describes the science drivers, conceptual design, observing modes, and expected performance of METIS.

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arXiv2021

Trajectory and orbit of the unique carbonaceous meteorite Flensburg

The C1-ungrouped carbonaceous chondrite Flensburg fell in Germany on September 12, 2019, in the daytime. We determined the atmospheric trajectory, velocity, and heliocentric orbit using one dedicated AllSky6 meteor camera and three casual video records of the bolide. It was found that the meteorite originated in the vicinity of the 5:2 resonance with Jupiter at heliocentric distance of 2.82 AU. When combined with the bolide energy reported by the U.S. Government sensors (USGS), the pre-atmospheric diameter of the meteoroid was estimated to 2 - 3 meters and the mass to 10,000 - 20,000 kg. The meteoroid fragmented heavily in the atmosphere at heights of 46 - 37 km, under dynamic pressures of 0.7 - 2 MPa. The recovery of just one meteorite suggests that only a very small part of the original mass reached the ground. The bolide velocity vector was compared with that reported by the USGS. There is good agreement in the radiant but the velocity value has been underestimated by the USGS by almost 1 km/s.

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arXiv2020

Detection of polarization neutral points in observations of the combined corona and sky during the 21 August 2017 total solar eclipse

We report the results of polarimetric observations of the total solar eclipse of 21 August 2017 from Rexburg, Idaho (USA). We use three synchronized DSLR cameras with polarization filters oriented at 0°, 60°, and 120° to provide high-dynamic-range RGB polarization images of the corona and surrounding sky. We measure tangential coronal polarization and vertical sky polarization, both as expected. These observations provide detailed detections of polarization neutral points above and below the eclipsed Sun where the coronal polarization is canceled by the sky polarization. We name these special polarization neutral points after Minnaert and Van de Hulst.

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arXiv2012

Ground-based search for the brightest transiting planets with the Multi-site All-Sky CAmeRA - MASCARA

The Multi-site All-sky CAmeRA MASCARA is an instrument concept consisting of several stations across the globe, with each station containing a battery of low-cost cameras to monitor the near-entire sky at each location. Once all stations have been installed, MASCARA will be able to provide a nearly 24-hr coverage of the complete dark sky, down to magnitude 8, at sub-minute cadence. Its purpose is to find the brightest transiting exoplanet systems, expected in the V=4-8 magnitude range - currently not probed by space- or ground-based surveys. The bright/nearby transiting planet systems, which MASCARA will discover, will be the key targets for detailed planet atmosphere observations. We present studies on the initial design of a MASCARA station, including the camera housing, domes, and computer equipment, and on the photometric stability of low-cost cameras showing that a precision of 0.3-1% per hour can be readily achieved. We plan to roll out the first MASCARA station before the end of 2013. A 5-station MASCARA can within two years discover up to a dozen of the brightest transiting planet systems in the sky.

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