arXiv subjects

Louis Desdoigts

Publications and source records attributed to Louis Desdoigts.

18 recordsLinked to original sources

arXiv2026

A Candidate Innermost Fifth Planet In the HR 8799 System Revealed By JWST NIRISS Aperture Masking Interferometry

We detect a candidate fifth planet in the HR 8799 system, directly imaged with the JWST/NIRISS Aperture Masking Interferometer (AMI). The detected source lies just above a $3\sigma$ contrast curve at a contrast of $\sim2\times10^{-4}$ in the F380M filter at a projected separation of $\sim150$ mas, corresponding to a few-to-several Jupiter mass planet at an orbital radius of $\sim 7$au. The separation of the candidate is compatible with absolute proper-motion constraints from Gaia and Hipparcos assuming it is bound, while its orbital position lies near a stable orbital solution of a fifth planet in a 3:1 mean motion resonance with planet e. This detection was made possible by a new JWST/NIRISS AMI data pipeline that reaches the photon noise limited potential of AMI by accounting for the optical and electronic systematics that limited sensitivity in prior analyses. Confirmation of this candidate would make HR 8799 the first directly imaged five-planet system and provide insight into the orbital dynamics and the dynamical evolution of planetary systems with widely-separated gas giants.

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arXiv2026

NEXT: The Netherlands EXoplanet Testbed I. Goals and opto-mechanical design

We report on the goals, design, and ongoing development of the Netherlands EXoplanet Testbed (NEXT), a high-contrast imaging testbed under construction in Leiden. NEXT is designed to develop and validate technologies and algorithms for extreme adaptive optics (XAO) and coronagraphy at the performance levels required by the next generation of high-contrast imagers on the Extremely Large Telescopes (ELTs) and future space observatories. All powered optics in the common path are custom off-axis parabolas, making the bench fully reflective up to the science cameras, and it operates from the visible to the near-infrared (500-1800 nm). It combines a woofer-tweeter XAO module, using an ALPAO woofer and a Boston Micromachines kilo-DM as tweeter, with a coronagraphic arm that supports common coronagraph architectures and focal-plane wavefront control for dark-hole digging, and reserves space for a suite of wavefront sensors. The design targets a raw contrast of $10^{-7}$ (goal: $10^{-8}$) at $5\lambda/D$ and 800 nm. We present the opto-mechanical design of the testbed, the key trade-offs made to reach these contrast levels, and Fresnel-propagation simulations of its predicted performance.

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arXiv2026

Forward modelling coronagraphic images with a fully physical, differentiable digital twin of MagAO-X: first laboratory results

Post-processing of high contrast imaging data relies on an accurate model of the stellar point spread function (PSF). Current techniques build this model from the science images themselves, using observational diversity (e.g., angular, spectral or polarimetric diversity), which can cause self-subtraction of the companion signal and constrains the observing strategy. Telemetry-based forward modelling instead builds the stellar PSF model from wavefront sensor data that is already recorded during the observation. The wavefront sensor measures the coherent starlight and can therefore be used to create a PSF model that only models the stellar light and does not reproduce the incoherent light of a companion. We present a fully physical and differentiable digital twin of the focal plane low-order wavefront sensor (FLOWFS) and the coronagraphic science beam of the MagAO-X instrument, implemented in \texttt{dLux}, and calibrate it on laboratory data. When fitted directly to the science images, the model reproduces the coronagraphic PSF down to the photon and read noise floor of the data. When instead forward modelled from the FLOWFS telemetry alone, the residuals reach $6\times10^{-5}$ of the stellar peak at $5\ \lambda/D$, a factor of 5 below the raw contrast, with the remaining residual set by how well the wavefront estimate transfers from the FLOWFS branch to the science branch of the model. An injected companion at $5\ \lambda/D$ with a peak contrast of $10^{-3}$ is recovered without measurable self-subtraction. We discuss the model improvements currently under development and the path towards on-sky validation.

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arXiv2026

The final design of GMagAO-X: the wavefront sensing and control (WFS&C) architecture of GMagAO-X

The Giant Magellan Adaptive Optics eXtreme (GMagAO-X) instrument has now been selected as an official part of the Giant Magellan Telescope's (GMT) instrument suite. The instrument will be ready at first-light of the GMT in the mid 2030s. The instrument is now progressing towards its final design with a final design review planned for March, 2027. The high-density actuator deformable mirror with 21.000 actuators will allow GMagAO-X to create diffraction-limited images from visible to near-infrared. GMagAO-X will be coupled with high-performance coronagraphs to search for exoplanets at the diffraction-limit. The coronagraphs require wavefront control at sub-nm precision. We will provide an update on the wavefront sensing and control architecture and how the loops interact with each other through end-to-end simulations.

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arXiv2026

ADORA: a differentiable optical modeling and astrometric retrieval framework for SHERA

Searching for Habitable Exoplanets with Relative Astrometry (SHERA) is a proposed Small Explorer mission concept designed to measure the separation of nearby binary stars at microarcsecond-class precision. Recovering this signal requires separating astrophysical motion from coupled changes in pointing, plate scale, wavefront error, spectral response, and detector calibration. We present the Astrometric Differentiable Optics and Retrieval Algorithm (ADORA), an image-domain framework that combines a three-plane differentiable physical-optics model with a layered astrometric inference algorithm. The forward model includes a diffractive pupil, mirror-specific wavefront error and beamwalk, polychromatic source and throughput models, and configurable detector effects. Per-frame registration states are treated locally and eliminated through Schur reduction before the slower astrometric and instrument state is updated in a prior-whitened Fisher eigenbasis. Five-minute matched-model simulations show no detected separation bias at the current Monte Carlo depth and approximately 11 uas realization-to-realization scatter. A SHERA target sweep reveals a more-than-fivefold variation in astrometric information between Alpha Centauri and 61 Cygni, motivating future target-dependent accumulation and update cadence. High-order-wavefront knowledge error can drive the retrieval toward a strongly biased astrometric solution while leaving the local posterior sigma nearly unchanged, demonstrating that statistical curvature alone does not capture unmodeled bias. Pixel-position errors across the tested range remain near the matched-model recovery scale indicating robustness to certain detector calibration errors. ADORA provides a flexible framework for studying astrometric extraction, calibration-bias diagnosis, and future SHERA requirements.

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arXiv2026

Searching for Habitable Exoplanets with Relative Astrometry (SHERA). I. The Case for Searching for Planets in Binary Star Systems

Discovering Earth-like planets orbiting Sun-like stars was identified as a priority science goal of the Astronomy 2020 Decadal Survey. It is confounded by many factors, one of which is the high multiplicity of Sun-like stars in the local neighborhood - half of nearby Sun-like stars are in binary or higher-order stellar systems, which are less amenable to the detection of small planets with almost all of the currently productive exoplanet detection techniques. Here we describe the SHERA (Searching for Habitable Exoplanets with Relative Astrometry) NASA Small Explorer mission concept. SHERA utilizes diffractive-pupil technology on a small, simple optical space telescope to achieve microarcsecond precision relative astrometry on 14 Sun-like stars in seven nearby multi-star systems, combining the pupil and stellar binarity to provide a precise reference in the image plane. With this precision, SHERA would enable: (i) a search for rocky planets in the habitable zones of the closest Sun-like stars; (ii) an investigation of the impact of binary star formation on small, widely separated planets; and (iii) the performance of crucial precursor observations on a number of high-priority targets of NASA's future missions to characterize Earth-like planets, such as the Habitable Worlds Observatory. When combined with radial velocity measurements, SHERA relative astrometry will also enable exploration of the three-dimensional orbital structure of planets in binary systems.

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arXiv2026

Tolerancing the PIAA-ZWFS: a practical and robust wavefront sensor that approaches the fundamental sensitivity limit

High-contrast imaging demands extremely sensitive wavefront sensing to correct atmospheric effects and surface errors. While the limits of the sensitivity of a wavefront sensor are well known, a practical, robust design that saturates these limits remains elusive. This work further investigates the PIAA-ZWFS (Phase-Induced Amplitude Apodization-Zernike Wavefront Sensor). In previous work, we developed a framework to optimise its design, maximising Fisher information per frame in the presence of phase aberrations. In these proceedings, we study the effect of various manufacturing and alignment errors in the system on the overall performance. We employ both traditional Monte Carlo sampling and a 2nd order expansion using our auto-differentiable simulator. The performance of the PIAA-ZWFS is not significantly degraded by these errors at values typical for manufacturing.

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arXiv2026

Calibration of an Analog-to-Digital Conversion Nonlinearity in JWST/NIRISS

We quantify an unusual flux-dependent systematic which is periodic in raw counts in flight data from the James Webb Space Telescope's Near Infrared Imager and Slitless Spectrograph (JWST/NIRISS), used extensively for exoplanet imaging and spectroscopy. Originally discovered in the aperture masking interferometry (AMI) mode, it also manifests in the Single Object Slitless Spectroscopy (SOSS) mode with the same dominant period of 1024 in raw analog-to-digital units (ADU). The likely cause of the signal is an analog-to-digital converter (ADC) integral nonlinearity (INL) in which case it will apply to all observations taken with the NIRISS instrument. Fortunately, it is straightforward to correct the data in postprocessing. The periodic INL is shown to be flux-dependent, increasing in amplitude with higher pixel counts on the detector. We derive a model of this periodic INL by fitting a combination of a polynomial and sinusoid multiplied with the residuals of ramp fits to the uncalibrated data and find an amplitude of 125ppm, up to a 2.5-count shift for a pixel with 20,000ADU. We apply this model to correct the well-studied NIRISS SOSS Program ERS1366 dataset of WASP-39b and reduce the data into a transmission spectrum. We find that our corrected transmission spectrum removes the INL systematic from the uncorrected spectrum at the 30ppm level across both orders, and also corrects a 55ppm offset between Order 1 and Order 2. We recommend a larger scale data-driven calibration of the periodic INL and the adoption of the outcome into NIRISS data pipelines.

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arXiv2026

Mitigating effects of telescope jitter through differentiable forward-modeling

Instabilities in telescope pointing, commonly referred to as jitter, introduce image degradation that can compromise the accuracy of critical scientific observables. This work presents a differentiable forward-modeling approach to both understand and mitigate the impact of jitter. We apply dLux -- a differentiable optical simulation framework built in the JAX numerical simulation framework -- to model the blurring effects of jitter on the final image. We categorize jitter into low-, medium-, and high-frequency regimes with respect to the camera frame rate and build simple jitter models based on its manifestation on the detector. The forward-model approach proves effective for low- and high-frequency regimes, but the inherent unpredictability of medium-frequency jitter may lead to model misspecification. As a test case we apply these models to the TOLIMAN mission, a forthcoming CubeSat telescope dedicated to detecting nearby Earth-analogue exoplanets through high-precision astrometry. Using Fisher information analysis, we quantify the effect of jitter on TOLIMAN's primary science observable -- the angular binary separation of the Alpha Centauri AB binary components. We find model misspecification does not introduce a systematic bias on the recovered binary separation except when fitting a one-dimensional jitter model to a two-dimensional motion, hence we recommend the use of a two-dimensional model. The forward-model approach offers a generalized method applicable to other telescope systems, including ongoing work with JWST's NIRISS instrument. This approach represents a significant step toward delivering higher accuracy measurements at modern observatories as demands on precision continue to rise.

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arXiv2026

The TOLIMAN mission: A low-cost space telescope for high precision narrow-angle astrometry

The TOLIMAN project is engaged with the construction, launch and operation of a low-cost space telescope of unorthodox optical design. Its primary science goal targets an exhaustive search for temperate-orbit rocky planets around either star in the alpha Centauri AB binary within our nearest-neighbor star system. Despite their favorable proximity and brightness, the detection of terrestrial exoplanets around such nearby Sun-like stars remains problematic for contemporary instrumental approaches. By performing narrow-angle astrometric monitoring of binary stars at extreme precision, any exoplanets will betray their presence by way of gravitationally-induced perturbations on the binary orbit. Recovery of this signal is challenging for it amounts to only a few microarcseconds of angular deflection (at best), and so is normally thought to require a large (meter-class) instrument. By implementing an innovative optical and signal encoding architecture, the TOLIMAN space telescope aims to recover such signals with a telescope aperture of only 12.5cm. This paper gives an overview of key features of the mission; in particular the concepts underlying the optics to enable image registration at the extreme levels of precision required. An outline is also provided, sketching further mission components and systems incorporated into the 16U CubeSat spacecraft bus in which the science payload is housed - all of which are now under construction.

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arXiv2025

Image reconstruction with the JWST Interferometer

Flying on board the James Webb Space Telescope (JWST) above Earth's turbulent atmosphere, the Aperture Masking Interferometer (AMI) on the NIRISS instrument is the highest-resolution infrared interferometer ever placed in space. However, its performance was found to be limited by non-linear detector systematics, particularly charge migration - or the Brighter-Fatter Effect. Conventional interferometric Fourier observables are degraded by non-linear transformations in the image plane, with the consequence that the inner working angle and contrast limits of AMI were seriously compromised. Building on the end-to-end differentiable model & calibration code amigo, we here present a regularised maximum-likelihood image reconstruction framework dorito which can deconvolve AMI images either in the image plane or from calibrated Fourier observables, achieving high angular resolution and contrast over a wider field of view than conventional interferometric limits. This modular code by default includes regularisation by maximum entropy, and total variation defined with $l_1$ or $l_2$ metrics. We present imaging results from dorito for three benchmark imaging datasets: the volcanoes of Jupiter's moon Io, the colliding-wind binary dust nebula WR 137 and the archetypal Seyfert 2 active galactic nucleus NGC 1068. In all three cases we recover images consistent with the literature at diffraction-limited resolutions. The performance, limitations, and future opportunities enabled by amigo for AMI imaging (and beyond) are discussed.

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arXiv2025

AMIGO: a Data-Driven Calibration of the JWST Interferometer

The James Webb Space Telescope (JWST) hosts a non-redundant Aperture Masking Interferometer (AMI) in its Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument, providing the only dedicated interferometric facility aboard - magnitudes more precise than any interferometric experiment previously flown. However, the performance of AMI (and other high resolution approaches such as kernel phase) in recovery of structure at high contrasts has not met design expectations. A major contributing factor has been the presence of uncorrected detector systematics, notably charge migration effects in the H2RG sensor, and insufficiently accurate mask metrology. Here we present Amigo, a data-driven calibration framework and analysis pipeline that forward-models the full JWST AMI system - including its optics, detector physics, and readout electronics - using an end-to-end differentiable architecture implemented in the Jax framework and in particular exploiting the dLux optical modelling package. Amigo directly models the generation of up-the-ramp detector reads, using an embedded neural sub-module to capture non-linear charge redistribution effects, enabling the optimal extraction of robust observables, for example kernel amplitudes and phases, while mitigating systematics such as the brighter-fatter effect. We demonstrate Amigo's capabilities by recovering the ABDor AC binary from commissioning data with high-precision astrometry, and detecting both HD206893B and the inner substellar companion HD206893c: a benchmark requiring contrasts approaching 10 magnitudes at separations of only 100 mas. These results exceed outcomes from all published pipelines, and re-establish AMI as a viable competitor for imaging at high contrast at the diffraction limit. Amigo is publicly available as open-source software community resource.

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arXiv2024

Differentiable Optics with dLux I: Deep calibration of Flat Field and Phase Retrieval with Automatic Differentiation

The sensitivity limits of space telescopes are imposed by uncalibrated errors in the point spread function, photon-noise, background light, and detector sensitivity. These are typically calibrated with specialized wavefront sensor hardware and with flat fields obtained on the ground or with calibration sources, but these leave vulnerabilities to residual time-varying or non-common path aberrations and variations in the detector conditions. It is therefore desirable to infer these from science data alone, facing the prohibitively high dimensional problems of phase retrieval and pixel-level calibration. We introduce a new Python package for physical optics simulation, dLux, which uses the machine learning framework JAX to achieve GPU acceleration and automatic differentiation (autodiff), and apply this to simulating astronomical imaging. In this first of a series of papers, we show that gradient descent enabled by autodiff can be used to simultaneously perform phase retrieval and calibration of detector sensitivity, scaling efficiently to inferring millions of parameters. This new framework enables high dimensional optimization and inference in data analysis and hardware design in astronomy and beyond, which we explore in subsequent papers in this series.

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arXiv2024

Differentiable Optics with dLux II: Optical Design Maximising Fisher Information

The design of astronomical hardware operating at the diffraction limit requires optimisation of physical optical simulations of the instrument with respect to desired figures of merit, such as photometric or astrometric precision. System design entails many parameters some of which may entangle the fidelity of science observables with strongly nonlinear dependencies upon instrument properties. Here we present a differentiable optical simulation framework dLux, a software library designed to construct optical models that are integrated with automatic differentiation. This approach enables the direct evaluation of gradients and higher-order derivatives through the forward model, facilitating statistically principled design and optimisation of instrument configurations. The methodology leverages numerically stable second- and higher-order derivatives to directly compute Fisher information and covariance forecasts, enabling efficient Bayesian experimental design targeted toward optimising abstracted figures of merit, such as the precision of parameters recovered through complex sets of operations. The method is validated against analytical results and applied to optimise the astrometric precision achievable with a parametrised telescope model and a diffractive pupil design relevant to exoplanet detection missions. To support reproducibility and facilitate methodological extension, we provide example implementations via open-source code on the Github sharing platform.

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arXiv2024

The James Webb Interferometer: Space-based interferometric detections of PDS 70 b and c at 4.8 $\mu$m

We observed the planet-hosting system PDS 70 with the James Webb Interferometer, JWST's Aperture Masking Interferometric (AMI) mode within NIRISS. Observing with the F480M filter centered at 4.8 $\mu$m, we simultaneously fit geometrical models to the outer disk and the two known planetary companions. We re-detect the protoplanets PDS 70 b and c at an SNR of 14.7 and 7.0, respectively. Our photometry of both PDS 70 b and c provides tentative evidence of mid-IR circumplanetary disk emission through fitting SED models to these new measurements and those found in the literature. We also newly detect emission within the disk gap at an SNR of $\sim$4, at a position angle of $220^{+10}_{-15}$ degrees, and an unconstrained separation within $\sim$200 mas. Follow-up observations will be needed to determine the nature of this emission. We place a 5$\sigma$ upper limit of 208 $\pm$ 10 $\mu$Jy on the flux of the candidate PDS 70 d at 4.8 $\mu$m, which indicates that if the previously observed emission at shorter wavelengths is due to a planet, this putative planet has a different atmospheric composition than PDS 70 b or c. Finally, we place upper limits on emission from any additional planets in the disk gap. We find an azimuthally averaged 5$\sigma$ contrast upper limit $>$7 magnitudes at separations greater than 110 mas. These are the deepest limits to date within $\sim$250 mas at 4.8 $\mu$m and the first space-based interferometric observations of this system.

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arXiv2022

The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- IV. Aperture Masking Interferometry

The James Webb Space Telescope's Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) flies a 7-hole non-redundant mask (NRM), the first such interferometer in space, operating at 3-5 \micron~wavelengths, and a bright limit of $\simeq 4$ magnitudes in W2. We describe the NIRISS Aperture Masking Interferometry (AMI) mode to help potential observers understand its underlying principles, present some sample science cases, explain its operational observing strategies, indicate how AMI proposals can be developed with data simulations, and how AMI data can be analyzed. We also present key results from commissioning AMI. Since the allied Kernel Phase Imaging (KPI) technique benefits from AMI operational strategies, we also cover NIRISS KPI methods and analysis techniques, including a new user-friendly KPI pipeline. The NIRISS KPI bright limit is $\simeq 8$ W2 magnitudes. AMI (and KPI) achieve an inner working angle of $\sim 70$ mas that is well inside the $\sim 400$ mas NIRCam inner working angle for its circular occulter coronagraphs at comparable wavelengths.

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arXiv2021

Phase Retrieval and Design with Automatic Differentiation

The principal limitation in many areas of astronomy, especially for directly imaging exoplanets, arises from instability in the point spread function (PSF) delivered by the telescope and instrument. To understand the transfer function, it is often necessary to infer a set of optical aberrations given only the intensity distribution on the sensor - the problem of phase retrieval. This can be important for post-processing of existing data, or for the design of optical phase masks to engineer PSFs optimized to achieve high contrast, angular resolution, or astrometric stability. By exploiting newly efficient and flexible technology for automatic differentiation, which in recent years has undergone rapid development driven by machine learning, we can perform both phase retrieval and design in a way that is systematic, user-friendly, fast, and effective. By using modern gradient descent techniques, this converges efficiently and is easily extended to incorporate constraints and regularization. We illustrate the wide-ranging potential for this approach using our new package, Morphine. Challenging applications performed with this code include precise phase retrieval for both discrete and continuous phase distributions, even where information has been censored such as heavily-saturated sensor data. We also show that the same algorithms can optimize continuous or binary phase masks that are competitive with existing best solutions for two example problems: an Apodizing Phase Plate (APP) coronagraph for exoplanet direct imaging, and a diffractive pupil for narrow-angle astrometry. The Morphine source code and examples are available open-source, with a similar interface to the popular physical optics package Poppy.

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arXiv2020

Periodic Astrometric Signal Recovery through Convolutional Autoencoders

Astrometric detection involves a precise measurement of stellar positions, and is widely regarded as the leading concept presently ready to find earth-mass planets in temperate orbits around nearby sun-like stars. The TOLIMAN space telescope[39] is a low-cost, agile mission concept dedicated to narrow-angle astrometric monitoring of bright binary stars. In particular the mission will be optimised to search for habitable-zone planets around Alpha Centauri AB. If the separation between these two stars can be monitored with sufficient precision, tiny perturbations due to the gravitational tug from an unseen planet can be witnessed and, given the configuration of the optical system, the scale of the shifts in the image plane are about one millionth of a pixel. Image registration at this level of precision has never been demonstrated (to our knowledge) in any setting within science. In this paper we demonstrate that a Deep Convolutional Auto-Encoder is able to retrieve such a signal from simplified simulations of the TOLIMAN data and we present the full experimental pipeline to recreate out experiments from the simulations to the signal analysis. In future works, all the more realistic sources of noise and systematic effects present in the real-world system will be injected into the simulations.

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