arXiv subjects

Sylvain Oberti

Publications and source records attributed to Sylvain Oberti.

18 recordsLinked to original sources

arXiv2026

MORFEO: Advancing Towards Final Design

The Multiconjugate adaptive Optics Relay For ELT Observations (MORFEO) is a first-generation adaptive optics module for the Extremely Large Telescope (ELT), designed to deliver a diffraction-limited, highly uniform 53x53 arcsec field of view to the MICADO near-infrared camera. As the project advances toward its Final Design Review (FDR), significant consolidations have been achieved across all subsystems. This paper presents an updated overview of the MORFEO system, highlighting its dual operational modes (MCAO and SCAO) and recent developments in its opto-mechanical architecture. We dedicate specific focus to the core adaptive hardware, detailing the fifth-generation post-focal deformable mirrors, the highly complex Laser Guide Star (LGS) objective zoom system required to track sodium layer variations, and the Natural Guide Star (NGS) low-order and reference sensing strategies. Furthermore, we detail the advanced pseudo-open-loop control strategy managed by a split Hard and Soft Real-Time Computer architecture. Finally, we report the latest end-to-end performance estimations obtained via the SPECULA simulation framework, demonstrating compliance with the stringent Strehl Ratio and sky coverage requirements under median atmospheric conditions.

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arXiv2026

Data-calibrated point spread function prediction: General description of the method and demonstration on MUSE-NFM

Precise knowledge of the point spread function (PSF) underpins many data analysis steps in astronomy, from photometry and astrometry to source de-blending and deconvolution. In adaptive optics (AO) observations, however, the PSF is highly variable with wavelength, field position, and observing conditions, making it difficult to model. Traditional PSF reconstruction (PSF-R) requires full AO telemetry and complex infrastructures, limiting its routine use, especially for tomographic systems. We present a practical framework for fast, accurate, and data-calibrated PSF modeling that captures the spatial and spectral variability of AO-corrected PSFs without relying on complete AO telemetry. Our approach builds on a Fourier-based PSF model inspired by astro-TIPTOP. As inputs, our model uses only a compact set of physically meaningful parameters retrievable from the ESO archive. A lightweight neural network corrects these inputs to achieve the best match with real data. It is trained end to end with the PSF model, allowing it to learn any miscalibrations directly from on-sky data. The framework achieves high accuracy on on-sky data. On a test set of MUSE-NFM standard stars, it yields median errors of 13.5% in the Strehl ratio and 10.9% in the core full width at half maximum (FWHM). In crowded MUSE-NFM observations of $\omega$ Centauri, the method predicts dozens of off-axis, wavelength-dependent PSFs with a Strehl error of <5% and a FWHM error of 4.6%, enabling source separation without per-star PSF extraction. Our compact, physics-informed, and data-calibrated model delivers accurate, polychromatic, and field-varying PSFs without relying on full AO telemetry. While demonstrated on MUSE-NFM, the method is still transferable to other AO-assisted instruments.

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arXiv2025

GRAVITY+ adaptive optics (GPAO) tests in Europe

We present in this proceeding the results of the test phase of the GRAVITY+ adaptive optics. This extreme AO will enable both high-dynamic range observations of faint companions (including exoplanets) thanks to a 40x40 sub-apertures wavefront control, and sensitive observations (including AGNs) thanks to the addition of a laser guide star to each UT of the VLT. This leap forward is made thanks to a mostly automated setup of the AO, including calibration of the NCPAs, that we tested in Europe on the UT+atmosphere simulator we built in Nice. We managed to reproduce in laboratory the expected performances of all the modes of the AO, including under non-optimal atmospheric or telescope alignment conditions, giving us the green light to proceed with the Assembly, Integration and Verification phase in Paranal.

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arXiv2024

Striving towards robust phase diversity on-sky: Implementing LIFT for VLT/MUSE-NFM

The recent IRLOS upgrade for VLT/MUSE narrow field mode (NFM) introduced a full-pupil mode to enhance sensitivity and sky coverage. This involved replacing the 2x2 Shack-Hartmann sensor with a single lens for full-aperture photon collection, which also enabled the engagement of the linearized focal-plane technique (LIFT) wavefront sensor instead. However, initial on-sky LIFT experiments have highlighted a complex point spread function (PSF) structure due to strong and polychromatic non-common path aberrations (NCPAs), complicating the accurate retrieval of tip-tilt and focus using LIFT. This study aims to conduct the first on-sky validation of LIFT on VLT/UT4, outline challenges encountered during the tests, and propose solutions for increasing the robustness of LIFT in on-sky operations. We developed a two-stage approach to focal-plane wavefront sensing, where tip-tilt and focus retrieval done with LIFT is preceded by the NCPA calibration step. The resulting NCPA estimate is subsequently used by LIFT. To perform the calibration, we proposed a method capable of retrieving the information about NCPAs directly from on-sky focal-plane PSFs. We verified the efficacy of this approach in simulated and on-sky tests. Our results demonstrate that adopting the two-stage approach has led to a significant improvement in the accuracy of the defocus estimation performed by LIFT, even under challenging low-flux conditions. The efficacy of LIFT as a slow and truth focus sensor in practical scenarios has been demonstrated. However, integrating NCPA calibration with LIFT is essential to verifying its practical application in the real system. Additionally, the proposed calibration step can serve as an independent and minimally invasive approach to evaluate NCPA on-sky.

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arXiv2023

MORFEO enters final design phase

MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations, formerly MAORY), the MCAO system for the ELT, will provide diffraction-limited optical quality to the large field camera MICADO. MORFEO has officially passed the Preliminary Design Review and it is entering the final design phase. We present the current status of the project, with a focus on the adaptive optics system aspects and expected milestones during the next project phase.

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arXiv2023

Non-modulated pyramid wavefront sensor: Use in sensing and correcting atmospheric turbulence

Context. The diffusion of adaptive optics systems in astronomical instrumentation for large ground-based telescopes is rapidly increasing and the pyramid wavefront sensor is replacing the Shack-Hartmann as the standard solution for single conjugate adaptive optics systems. The pyramid wavefront sensor is typically used with a tip-tilt modulation to increase the linearity range of the sensor, but the non-modulated case is interesting because it maximizes the sensor sensitivity. The latter case is generally avoided for the reduced linearity range that prevents robust operation in the presence of atmospheric turbulence. Aims. We aim to solve part of the issues of the non-modulated pyramid wavefront sensor by reducing the model error in the interaction matrix. We linearize the sensor response in the working conditions without extending the sensor linearity range. Methods. We developed a new calibration approach to model the response of pyramid wave front sensor in partial correction, whereby the working conditions in the presence of residual turbulence are considered. Results. We use in simulations to show how the new calibration approach allows for the pyramid wave front sensor without modulation to be used to sense and correct atmospheric turbulence and we discuss when this case is preferable over the modulated case.

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arXiv2023

The ESO's Extremely Large Telescope Working Groups

Since 2005 ESO has been working with its community and industry to develop an extremely large optical/infrared telescope. ESO's Extremely Large Telescope, or ELT for short, is a revolutionary ground-based telescope that will have a 39-metre main mirror and will be the largest visible and infrared light telescope in the world. To address specific topics that are needed for the science operations and calibrations of the telescope, thirteen specific working groups were created to coordinate the effort between ESO, the instrument consortia, and the wider community. We describe here the goals of these working groups as well as their achievements so far.

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arXiv2023

The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.

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arXiv2022

Super-resolution wavefront reconstruction

Super-Resolution (SR) is a technique that seeks to upscale the resolution of a set of measured signals. SR retrieves higher-frequency signal content by combining multiple lower resolution sampled data sets. SR is well known both in the temporal and spatial domains. It is widely used in imaging to reduce aliasing and enhance the resolution of coarsely sampled images.This paper applies the SR technique to the bi-dimensional wavefront reconstruction. In particular, we show how SR is intrinsically suited for tomographic multi WaveFront Sensor (WFS) AO systems revealing many of its advantages with minimal design effort. This paper provides a direct space and Fourier-optics description of the wavefront sensing operation and demonstrate how SR can be exploited through signal reconstruction, especially in the framework of Periodic Nonuniform Sampling. Both meta uniform and nonuniform sampling schemes are investigated. Then, the SR bi-dimensional model for a Shack Hartmann (SH) WFS is provided and the characteristics of the sensitivity function are analyzed. The SR concept is finally validated with numerical simulations of representative multi WFS SH AO systems. Our results show that combining several WFS samples in a SR framework grants access to a larger number of modes than the native one offered by a single WFS and that despite the fixed sub-aperture size across samples. Furthermore, we show that the associated noise propagation is not degraded under SR. Finally, the concept is extended to the signal produced by single Pyramid WFS. In conclusion, SR applied to wavefront reconstruction offers a new parameter space to explore as it decouples the size of the subaperture from the desired wavefront sampling resolution. By cutting short with old assumptions, new, more flexible and better performing AO designs become now possible.

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arXiv2022

Key wavefront sensors features for laser-assisted tomographic adaptive optics systems on the Extremely Large Telescope

Laser guide star (LGS) wave-front sensing (LGSWFS) is a key element of tomographic adaptive optics system. However, when considering Extremely Large Telescope (ELT) scales, the LGS spot elongation becomes so large that it challenges the standard recipes to design LGSWFS. For classical Shack-Hartmann wave-front sensor (SHWFS), which is the current baseline for all ELT LGS-assisted instruments, a trade-off between the pupil spatial sampling [number of sub-apertures (SAs)], the SA field-of-view (FoV) and the pixel sampling within each SA is required. For ELT scales, this trade-off is also driven by strong technical constraints, especially concerning the available detectors and in particular their number of pixels. For SHWFS, a larger field of view per SA allows mitigating the LGS spot truncation, which represents a severe loss of performance due to measurement biases. For a given number of available detectors pixels, the SA FoV is competing with the proper sampling of the LGS spots, and/or the total number of SAs. We proposed a sensitivity analysis, and we explore how these parameters impacts the final performance. In particular, we introduce the concept of super resolution, which allows one to reduce the pupil sampling per WFS and opens an opportunity to propose potential LGSWFS designs providing the best performance for ELT scales.

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arXiv2022

Infrared tip-tilt sensing: on-sky experience, lessons learned and unsolved problems

Infrared tip-tilt sensors (IR TTSs) have been deployed on three different laser guide star adaptive optics (AO) systems on three different telescopes. These IR TTS benefit from the high-order loop PSF sharpening in the near infrared, hence they provide a low tip-tilt residual and a good sky coverage. Nevertheless, these IR TTS are challenging and their use in AO is limited. In this paper, we outline existing IR TTS, provide on-sky performance results and describe our experience using IR TTS and along with plans for the near future. The second part of the paper deals with unresolved challenges for IR TTS. These include algorithms and loop stability in the low Strehl regime, using IR TTSs to measure higher-order modes and guiding on multiple guide stars with different magnitudes.

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arXiv2021

Instrumentation for ESO's Extremely Large Telescope

Design and construction of the instruments for ESO's Extremely Large Telescope (ELT) began in 2015. We present here a brief overview of the status of the ELT Instrumentation Plan. Dedicated articles on each instrument are presented elsewhere this volume.

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arXiv2020

Adaptive optics design status of MAORY, the MCAO system of European ELT

MAORY is the Multi-conjugate Adaptive Optics RelaY for the European ELT aimed at providing a 1 arcmin corrected field to MICADO, a near-infrared spectro-imager with a focus on astrometry. In this paper we re-view the main requirements and analysis that justify the current adaptive optics architecture and subsystem requirements. We discuss the wavefront error budget allocation focusing on the worst offenders terms and on a statistical analysis of their dependence on atmospheric and sodium profiles. We present an updated revision of the trade-off studies on the main AO parameters that, along with considerations coming from optical and mechanical subsystems, are used to define the preliminary design of the instrument.

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arXiv2020

MAORY AO performances

The Multi-conjugate Adaptive Optics RelaY (MAORY) should provide 30% SR in K band (50% goal) on half of the sky at the South Galactic Pole. Assessing its performance and the sensitivity to parameter variations during the design phase is a fundamental step for the engineering of such a complex system. This step, centered on numerical simulations, is the connection between the performance requirements and the Adaptive Optics system configuration. In this work we present MAORY configuration and performance and we justify theAdaptive Optics system design choices.

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arXiv2019

Physics-based model of the adaptive-optics corrected point-spread-function

Context. Adaptive optics (AO) systems greatly increase the resolution of large telescopes, but produce complex point spread function (PSF) shapes, varying in time and across the field of view. This PSF must be accurately known since it provides crucial information about optical systems for design, characterisation, diagnostics and image post processing. Aims. We develop here a model of the AO long exposure PSF, adapted to various seeing conditions and any AO system. This model is made to match accurately both the core of the PSF and its turbulent halo. Methods. The PSF model we develop is based on a parsimonious parameterization of the phase power spectral density with only five parameters to describe circularly symmetric PSFs and seven parameters for asymmetrical ones. Moreover, one of the parameters is directly the Fried parameter r0 of the turbulence s strength. This physical parameter is an asset in the PSF model since it can be correlated with external measurements of the r0, such as phase slopes from the AO real time computer (RTC) or site seeing monitoring. Results. We fit our model against endtoend simulated PSFs using OOMAO tool, and against on sky PSFs from the SPHERE ZIMPOL imager and the MUSE integral field spectrometer working in AO narrowfield mode. Our model matches the shape of the AO PSF both in the core and the halo, with a sub 1 percent relative error for simulated and experimental data. We also show that we retrieve the r0 parameter with subcentimeter precision on simulated data. For ZIMPOL data, we show a correlation of 97 percent between our r0 estimation and the RTC estimation. Finally, MUSE allows us to test the spectral dependency of the fitted r0 parameter. It follows the theoretical $λ^{6/5}$ evolution with a standard deviation of 0.3 cm. Evolution of other PSF parameters, such as residual phase variance or aliasing, is also discussed.

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arXiv2018

Multiple Star Systems in the Orion Nebula

This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium Cluster with the recently comissioned GRAVITY instrument. We observe a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for $θ^1$ Ori B, $θ^2$ Ori B, and $θ^2$ Ori C. We determine a separation for the previously suspected companion of NU Ori. We confirm four companions for $θ^1$ Ori A, $θ^1$ Ori C, $θ^1$ Ori D, and $θ^2$ Ori A, all with substantially improved astrometry and photometric mass estimates. We refine the orbit of the eccentric high-mass binary $θ^1$ Ori C and we are able to derive a new orbit for $θ^1$ Ori D. We find a system mass of 21.7 $M_{\odot}$ and a period of $53$ days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about 2, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints towards a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We exclude collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.

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arXiv2016

The numerical simulation tool for the MAORY multiconjugate adaptive optics system

The Multiconjugate Adaptive Optics RelaY (MAORY) is and Adaptive Optics module to be mounted on the ESO European-Extremely Large Telescope (E-ELT). It is a hybrid Natural and Laser Guide System that will perform the correction of the atmospheric turbulence volume above the telescope feeding the Multi-AO Imaging Camera for Deep Observations Near Infrared spectro-imager (MICADO). We developed an end-to-end Monte- Carlo adaptive optics simulation tool to investigate the performance of a the MAORY and the calibration, acquisition, operation strategies. MAORY will implement Multiconjugate Adaptive Optics combining Laser Guide Stars (LGS) and Natural Guide Stars (NGS) measurements. The simulation tool implements the various aspect of the MAORY in an end to end fashion. The code has been developed using IDL and uses libraries in C++ and CUDA for efficiency improvements. Here we recall the code architecture, we describe the modeled instrument components and the control strategies implemented in the code.

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arXiv2009

Layer Oriented Wavefront sensor for MAD on Sky operations

The Multiconjugate Adaptive optics Demonstrator (MAD) has successfully demonstrated on sky both Star Oriented (SO) and Layer Oriented (LO) multiconjugate adaptive optics techniques. While SO has been realized using 3 Shack-Hartmann wavefront sensors (WFS), we designed a multi-pyramid WFS for the LO. The MAD bench accommodates both WFSs and a selecting mirror allows choosing which sensor to use. In the LO approach up to 8 pyramids can be placed on as many reference stars and their light is co-added optically on two different CCDs conjugated at ground and to an high layer. In this paper we discuss LO commissioning phase and on sky operations.

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