arXiv subjects

Faustine Cantalloube

Publications and source records attributed to Faustine Cantalloube.

At least 19 recordsLinked to original sources

arXiv2026

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems VIII: patchy forsterite and enstatite clouds in the atmosphere of VHS 1256 b, retrieval lessons learned and outlook to the future

JWST defines a new era for the data-driven approach of retrieval modelling, which has become a cornerstone tool for the statistical inference of exoplanetary and brown dwarf properties. The Early Release Science program #1386 observations of VHS 1256 b represent a huge jump in data quality, data quantity and spectral coverage for such objects. VHS 1256 b is a young, planetary mass and extremely variable companion that populates the enigmatic L/T cohort of substellar atmospheres. In this first retrieval analysis of the full 1 - 18 micron dataset, we apply the Brewster retrieval framework to the NIRSpec and MIRI spectroscopic observations of VHS 1256 b, exploring a variety of cloud species and structures. Using Delta(BIC) we find that the data is best described by a forsterite (Mg$_{2}$SiO$_{4}$) and enstatite (MgSiO$_{3}$) cloud combination. Our analysis shows a strong preference for patchy silicate cloud coverage, which aligns with VHS 1256 b's extensive and well documented spectral variability. Our retrieval is able to place constraints on the abundances of H$_{2}$O, CO, CO$_{2}$, CH$_{4}$ as well as NH$_{3}$. We also show that the retrieved parameters are sensitive to the data used and the relative signal-to-noise ratios between data from different instruments. We conclude with the next steps for the wider retrieval community to better understand young and cloudy exoplanetary atmospheres.

astro-ph.EP↗

arXiv2026

SF2A Environmental Transition Commission: Chosen pieces from the survey 'French astronomy and astrophysics research activities in the face of the environmental crisis, from 2019 to 2024'

In 2025, the French Society for Astronomy \& Astrophysics (SF2A), gave the environmental transition commission the opportunity to share their considerations during a plenary session at the annual SF2A conference. This year, the presentation focused on some of the main results obtained from the survey entitled 'French astronomy and astrophysics research activities in the face of the environmental crisis, from 2019 to 2024'. The survey was initiated in 2019 by the group 'Environnement-Transition' (coordinated by P. Martin) at IRAP, whose results were presented during the SF2A annual conference 2019 in Nice. The survey was updated in 2024 by the CNRS INSU-AA prospective working group 'Climate and ecological challenge' (coordinated by S. Bontemp). The SF2A environmental transition commission took on the survey to the French institutes, sorted the answers and extracted the preliminary results. The full results will be published at the end of 2025 in the final CNRS INSU-AA 2024 prospective document. This publication presents a selection of pieces from the full survey, along with a few of the main discussions it triggers.

physics.soc-ph↗

arXiv2026

SF2A Environmental Transition Commission: Summary of the 2025 workshop

During its annual conference in 2025, the French Society of Astronomy \& Astrophysics (SF2A) hosted, for the fifth time, a special session dedicated to discussing the environmental transition within the French A\&A research community. During the 2025 workshop, the goal was to review four contemporary topics within the context of environmental transition actions and discussions: (1) institutional actions, (2) the early-career researchers singularity, (3) research infrastructures and tools, and (4) the geopolitical conditions under which A\&A research remains possible. The workshop concluded with a round-table discussion that brought together the various speakers so that every participant could express their ideas.

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arXiv2025

Keplerian motion of a compact source orbiting the inner disc of PDS 70: a third protoplanet in resonance with b and c?

The disc around PDS 70 hosts two directly imaged protoplanets in a gap. Previous VLT/SPHERE and recent James Webb Space Telescope/NIRCam observations have hinted at the presence of a third compact source in the same gap at ~13 au, interior to the orbit of PDS 70 b. We reduce seven published and one unpublished VLT/SPHERE datasets in YJH and K bands, as well as an archival VLT/NaCo dataset in L' band, and an archival VLT/SINFONI dataset in H+K band. We combine angular-, spectral- and reference star differential imaging to search for protoplanet candidates. We recover the compact source in all epochs, consistent with the JWST detection, moving on an arc that can be fit by Keplerian motion of a protoplanet which could be in a resonance with PDS 70 b & c. We find that the spectral slope is overall consistent with the unresolved star and inner disc emission at 0.95--1.65$μ$m, which suggests a dust scattering dominated spectrum. An excess beyond 2.3$μ$m could be thermal emission from either a protoplanet or heated circumplanetary dust, variability, or inner disc contamination, and requires confirmation. While we currently cannot rule out a moving inner disc feature or a dust clump associated with an unseen planet, the data supports the hypothesis of a third protoplanet in this remarkable system.

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arXiv2025

Use the 4S (Signal-Safe Speckle Subtraction): Explainable Machine Learning reveals the Giant Exoplanet AF Lep b in High-Contrast Imaging Data from 2011

The main challenge of exoplanet high-contrast imaging (HCI) is to separate the signal of exoplanets from their host stars, which are many orders of magnitude brighter. HCI for ground-based observations is further exacerbated by speckle noise originating from perturbations in Earth's atmosphere and imperfections in the telescope optics. Various data post-processing techniques are used to remove this speckle noise and reveal the faint planet signal. Often, however, a significant part of the planet signal is accidentally subtracted together with the noise. In the present work, we use explainable machine learning to investigate the reason for the loss of the planet signal for one of the most used post-processing methods: principal component analysis (PCA). We find that PCA learns the shape of the telescope point spread function for high numbers of PCA components. This representation of the noise captures not only the speckle noise but also the characteristic shape of the planet signal. Building on these insights, we develop a new post-processing method (4S) that constrains the noise model to minimize this signal loss. We apply our model to 11 archival HCI datasets from the VLT-NACO instrument in the L'-band and find that our model consistently outperforms PCA. The improvement is largest at close separations to the star ($\leq 4 λ/D$) providing up to 1.5 magnitudes deeper contrast. This enhancement enables us to detect the exoplanet AF Lep b in data from 2011, 11 years before its subsequent discovery. We present updated orbital parameters for this object.

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arXiv2025

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems III: Aperture Masking Interferometric Observations of the star HIP 65426 at 3.8 um

We present aperture masking interferometry (AMI) observations of the star HIP 65426 at $3.8\,\rm{μm}$ as a part of the JWST Direct Imaging Early Release Science (ERS) program obtained using the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument. This mode provides access to very small inner working angles (even separations slightly below the Michelson limit of $0.5λ/D$ for an interferometer), which are inaccessible with the classical inner working angles of the JWST coronagraphs. When combined with JWST's unprecedented infrared sensitivity, this mode has the potential to probe a new portion of parameter space across a wide array of astronomical observations. Using this mode, we are able to achieve a $5σ$ contrast of $Δm{\sim}7.62{\pm}0.13$ mag relative to the host star at separations ${\gtrsim}0.07{"}$, and the contrast deteriorates steeply at separations ${\lesssim}0.07{"}$. However, we detect no additional companions interior to the known companion HIP 65426 b (at separation ${\sim}0.82{"}$ or, $87^{+108}_{-31}\,\rm{au}$). Our observations thus rule out companions more massive than $10{-}12\,\rm{M_{Jup}}$ at separations ${\sim}10{-}20\,\rm{au}$ from HIP 65426, a region out of reach of ground or space-based coronagraphic imaging. These observations confirm that the AMI mode on JWST is sensitive to planetary mass companions at close-in separations (${\gtrsim}0.07{"}$), even for thousands of more distant stars at $\sim$100 pc, in addition to the stars in the nearby young moving groups as stated in previous works. This result will allow the planning and successful execution of future observations to probe the inner regions of nearby stellar systems, opening an essentially unexplored parameter space.

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arXiv2024

SF2A Environmental Transition Commission: Towards a desirable future for research in astronomy

During its annual conference in 2024, the French Society of Astronomy & Astrophysics (SF2A) hosted a special session dedicated to discussing the environmental transition within the scope of our occupation. Since 2021, thinking on this subject has progressed significantly, both quantitatively and qualitatively. This year was an opportunity to take stock of the main areas of reflection that we need to keep in mind in order to implement a fair, collective and effective environmental transition. This proceeding summarizes the key points from the plenary session related to the environmental transition special session. The purpose of the messages disseminated here is to suggest ideas for reflection and inspiration, so as to initiate, stimulate, and foster discussions within the A&A research community, towards the implementation of concrete measures to mitigate our environmental footprint.

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arXiv2024

Exoplanet Imaging Data Challenge, phase II: Comparison of algorithms in terms of characterization capabilities

In this communication, we report on the results of the second phase of the Exoplanet Imaging Data Challenge started in 2019. This second phase focuses on the characterization of point sources (exoplanet signals) within multispectral high-contrast images from ground-based telescopes. We collected eight data sets from two high-contrast integral field spectrographs (namely Gemini-S/GPI and VLT/SPHERE-IFS) that we calibrated homogeneously, and in which we injected a handful of synthetic planetary signals (ground truth) to be characterized by the data challenge participants. The tasks of the participants consist of (1) extracting the precise astrometry of each injected planetary signals, and (2) extracting the precise spectro-photometry of each injected planetary signal. Additionally, the participants may provide the 1-sigma uncertainties on their estimation for further analyses. When available, the participants can also provide the posterior distribution used to estimate the position/spectrum and uncertainties. The data are permanently available on a Zenodo repository and the participants can submit their results through the EvalAI platform. The EvalAI submission platform opened on April 2022 and closed on the 31st of May 2024. In total, we received 4 valid submissions for the astrometry estimation and 4 valid submissions for the spectrophotometry (each submission, corresponding to one pipeline, has been submitted by a unique participant). In this communication, we present an analysis and interpretation of the results.

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arXiv2024

An Alternating Minimization Algorithm with Trajectory for Direct Exoplanet Detection -- The AMAT Algorithm

Effective image post-processing algorithms are vital for the successful direct imaging of exoplanets. Standard PSF subtraction methods use techniques based on a low-rank approximation to separate the rotating planet signal from the quasi-static speckles, and rely on signal-to-noise ratio maps to detect the planet. These steps do not interact or feed each other, leading to potential limitations in the accuracy and efficiency of exoplanet detection. We aim to develop a novel approach that iteratively finds the flux of the planet and the low-rank approximation of quasi-static signals, in an attempt to improve upon current PSF subtraction techniques. In this study, we extend the standard L2 norm minimization paradigm to an L1 norm minimization framework to better account for noise statistics in the high contrast images. Then, we propose a new method, referred to as Alternating Minimization Algorithm with Trajectory, that makes a more advanced use of estimating the low-rank approximation of the speckle field and the planet flux by alternating between them and utilizing both L1 and L2 norms. For the L1 norm minimization, we propose using L1 norm low-rank approximation, a low-rank approximation computed using an exact block-cyclic coordinate descent method, while we use randomized singular value decomposition for the L2 norm minimization. Additionally, we enhance the visibility of the planet signal using a likelihood ratio as a postprocessing step. Numerical experiments performed on a VLT/SPHERE-IRDIS dataset show the potential of AMAT to improve upon the existing approaches in terms of higher S/N, sensitivity limits, and ROC curves. Moreover, for a systematic comparison, we used datasets from the exoplanet data challenge to compare our algorithm to other algorithms in the challenge, and AMAT with likelihood ratio map performs better than most algorithms tested on the exoplanet data challenge.

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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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arXiv2024

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems IV: NIRISS Aperture Masking Interferometry Performance and Lessons Learned

We present a performance analysis for the aperture masking interferometry (AMI) mode on board the James Webb Space Telescope Near Infrared Imager and Slitless Spectrograph (JWST/NIRISS). Thanks to self-calibrating observables, AMI accesses inner working angles down to and even within the classical diffraction limit. The scientific potential of this mode has recently been demonstrated by the Early Release Science (ERS) 1386 program with a deep search for close-in companions in the HIP 65426 exoplanetary system. As part of ERS 1386, we use the same data set to explore the random, static, and calibration errors of NIRISS AMI observables. We compare the observed noise properties and achievable contrast to theoretical predictions. We explore possible sources of calibration errors and show that differences in charge migration between the observations of HIP 65426 and point-spread function calibration stars can account for the achieved contrast curves. Lastly, we use self-calibration tests to demonstrate that with adequate calibration NIRISS F380M AMI can reach contrast levels of $\sim9-10$ mag at $\gtrsim λ/D$. These tests lead us to observation planning recommendations and strongly motivate future studies aimed at producing sophisticated calibration strategies taking these systematic effects into account. This will unlock the unprecedented capabilities of JWST/NIRISS AMI, with sensitivity to significantly colder, lower-mass exoplanets than lower-contrast ground-based AMI setups, at orbital separations inaccessible to JWST coronagraphy.

astro-ph.EP↗

arXiv2024

Searching for low-mass companions at small separations in transition disks with aperture masking interferometry

Transition disks have large central cavities that have been spatially resolved during recent years. Cavities and other substructures in circumstellar disks are often interpreted as signposts to massive companions. We aim to search for stellar and substellar companions in the central regions of transition disks. We want to determine if these disks might be circumbinary in their nature, similar to the HD 142527 system. We observed four systems, HD 100453, HD 100546, HD 135344 B, and PDS 70, with the sparse aperture masking mode of VLT/SPHERE. We extracted the complex visibilities and bispectra from the H2 and H3 imaging data. A binary model was fit to the closure phases to search for companions and estimate detection limits. For validation, we also analyzed four archival datasets of HD 142527 and inferred the orbital elements and atmospheric parameters of its low-mass stellar companion. We have not detected any significant point sources in the four observed systems. With a contrast sensitivity of $\approx$0.004, we can rule out stellar companions down to $\approx$2 au and partially explore the substellar regime at separations $\gtrsim$3-5 au. The analysis of HD 142527 B revealed that its projected orbit is aligned with dust features in the extended inner disk and that the orbit could be close to coplanar with the outer disk. Atmospheric modeling confirms the low-gravity and slightly reddened spectral appearance. The bulk parameters are in agreement with dynamical constraints and evolutionary tracks. In contrast to HD 142527, we find no evidence that a close-in stellar companion is responsible for the resolved disk features of HD 100453, HD 100546, HD 135344 B, and PDS 70. Instead, the formation of giant planets or even low-mass brown dwarfs could be shaping the innermost environment ($\lesssim$20 au) of these circumstellar disks, as is the case with the planetary system of PDS 70.

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arXiv2024

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems V: Do Self-Consistent Atmospheric Models Represent JWST Spectra? A Showcase With VHS 1256 b

The unprecedented medium-resolution (R~1500-3500) near- and mid-infrared (1-18um) spectrum provided by JWST for the young (140+/-20Myr) low-mass (12-20MJup) L-T transition (L7) companion VHS1256b gives access to a catalogue of molecular absorptions. In this study, we present a comprehensive analysis of this dataset utilizing a forward modelling approach, applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: Teff, log(g), [M/H], C/O, gamma, fsed, and R. Our findings reveal that each parameter's estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS1256b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a Teff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST's data for VHS1256b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.

astro-ph.EP↗

arXiv2023

Simulating METIS SCAO System

METIS, the Mid-Infrared ELT Imager and Spectrograph, is one of the four first-generation ELT instruments scheduled to see first light in 2028. Its two main science modules are supported by an adaptive optics system featuring a pyramid sensor with 90x90 subapertures working in the H and K bands. During the PDR and FDR phases, extensive simulations were carried out to support the sensing, reconstruction, and control concept of METIS single-conjugate adaptive optics (SCAO) system. We present details on the implementation of the COMPASS-based environment used for the simulations, the metrics used for analyzing our performance expectations, an overview of the main results, and some details on special cases like non-common path aberrations (NCPA) and water vapor seeing, as well as the low-wind effect.

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arXiv2023

Environmental transition: overview of actions to reduce the environmental footprint of astronomy

To keep current global warming below 1.5°C compared with the pre-industrial era, measures must be taken as quickly as possible in all spheres of society. Astronomy must also make its contribution. In this proceeding, and during the workshop to which it refers, different levers of actions are discussed through various examples: individual efforts, laboratory-level actions, impact evaluation and mitigation in major projects, institutional level, and involvement through collectives.

astro-ph.IM↗

arXiv2023

The debris disc of HD 131488 -- Bringing together thermal emission and scattered light

We show the first SPHERE/IRDIS and IFS data of the CO-rich debris disc around HD 131488. We use N-body simulations to model both the scattered light images and the SED of the disc in a self-consistent way. We apply the Henyey-Greenstein approximation, Mie theory, and the Discrete Dipole Approximation to model the emission of individual dust grains. Our study shows that only when gas drag is taken into account can we find a model that is consistent with scattered light as well as thermal emission data of the disc. The models suggest a gas surface density of $2\times10^{-5}\,M_\oplus/$au$^2$ which is in agreement with estimates from ALMA observations. Thus, our modelling procedure allows us to roughly constrain the expected amount of gas in a debris disc without actual gas measurements. We also show that the shallow size distribution of the dust leads to a significant contribution of large particles to the overall amount of scattered light. The scattering phase function indicates a dust porosity of $\sim0.2\ldots 0.6$ which is in agreement with a pebble pile scenario for planetesimal growth.

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arXiv2023

Impacts of high-contrast image processing on atmospheric retrievals

Many post-processing algorithms have been developed in order to better separate the signal of a companion from the bright light of the host star, but the effect of such algorithms on the shape of exoplanet spectra extracted from integral field spectrograph data is poorly understood. The resulting spectra are affected by noise that is correlated in wavelength space due to both optical and data processing effects. Within the framework of Bayesian atmospheric retrievals, we aim to understand how these correlations and other systematic effects impact the inferred physical parameters. We consider three algorithms (KLIP, PynPoint and ANDROMEDA), optimizing the choice of algorithmic parameters using a series of injection tests into archival SPHERE and GPI data of the HR 8799 system. The wavelength-dependent covariance matrix is calculated to provide a measure of instrumental and algorithmic systematics. We perform atmospheric retrievals using petitRADTRANS on optimally extracted spectra to measure how these data processing systematics influence the retrieved parameter distributions. The choice of data processing algorithm and parameters significantly impact the accuracy of retrieval results, with the mean posterior parameter bias ranging from 1 to 3 $σ$ from the true input parameters. Including the full covariance matrix in the likelihood improves the accuracy of inferred parameters, and cannot be accounted for using ad hoc scaling parameters in the retrieval framework. Using the Bayesian information criterion and other statistical measures as a heuristic goodness-of-fit metrics, the retrievals including the full covariance matrix are favoured when compared to using only the diagonal elements.

astro-ph.EP↗

arXiv2023

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems I: High Contrast Imaging of the Exoplanet HIP 65426 b from 2-16 $μ$m

We present JWST Early Release Science (ERS) coronagraphic observations of the super-Jupiter exoplanet, HIP 65426 b, with the Near-Infrared Camera (NIRCam) from 2-5 $μ$m, and with the Mid-Infrared Instrument (MIRI) from 11-16 $μ$m. At a separation of $\sim$0.82" (86$^{+116}_{-31}$ au), HIP 65426 b is clearly detected in all seven of our observational filters, representing the first images of an exoplanet to be obtained by JWST, and the first ever direct detection of an exoplanet beyond 5 $μ$m. These observations demonstrate that JWST is exceeding its nominal predicted performance by up to a factor of 10, depending on separation and subtraction method, with measured 5$σ$ contrast limits of $\sim$1$\times10^{-5}$ and $\sim$2$\times10^{-4}$ at 1" for NIRCam at 4.4 $μ$m and MIRI at 11.3 $μ$m, respectively. These contrast limits provide sensitivity to sub-Jupiter companions with masses as low as 0.3$M_\mathrm{Jup}$ beyond separations of $\sim$100 au. Together with existing ground-based near-infrared data, the JWST photometry are well fit by a BT-SETTL atmospheric model from 1-16 $μ$m, and span $\sim$97% of HIP 65426 b's luminous range. Independent of the choice of model atmosphere we measure an empirical bolometric luminosity that is tightly constrained between $\mathrm{log}\!\left(L_\mathrm{bol}/L_{\odot}\right)$=-4.31 to $-$4.14, which in turn provides a robust mass constraint of 7.1$\pm$1.2 $M_\mathrm{Jup}$. In totality, these observations confirm that JWST presents a powerful and exciting opportunity to characterise the population of exoplanets amenable to high-contrast imaging in greater detail.

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