Olivier Absil

Context . The SPHERE High-contrast Imaging survey for Exoplanets (SHINE) represents one of the largest and most sensitive direct imaging campaigns conducted to date with the VLT, targeting over 400 young, nearby stars with the goal of detecting and characterizing giant exoplanets and brown dwarfs. This extensive dataset offers a unique opportunity to revisit observations using modern, data-driven approaches, potentially uncovering new substellar candidates that may have been overlooked by classical analysis techniques. Aims . In this context, our study focuses on reprocessing and re-analysing the so-called F150 sample, a well-defined subset of 150 main-sequence stars within 100 pc observed in the H band with VLT/SPHERE as part of the SHINE survey. Methods . We applied NA-SODINN , a supervised deep learning model specifically tailored for detecting faint planetary signals in angular differential imaging sequences. Designed to model local noise properties by capturing spatio-temporal correlations, NA-SODINN produces network-confidence detection maps that push the detection of faint companions closer to the noise floor than classical S/N-based approaches. To translate the model’s pixel-wise confidence maps into actionable detections, we introduced a novel thresholding strategy that selects, for each annulus, the confidence threshold maximizing the F ₁ score (the harmonic mean of precision and recall) from injection-recovery experiments. This principled approach balances sensitivity and specificity, addressing a key limitation in current deep learning-based methods. Results . NA-SODINN recovers all known companions and some of the debris disks in the F150 sample, and it identifies 13 new substellar candidates not reported in previous studies: ten detected in both the H 2 and H 3 bands, and three in only one band. For the ten sources detected in both bands, we used the H 2– H 3 colour–magnitude diagram to perform a first assessment of their nature. Based on this analysis, we identified two ambiguous cases and three photometrically promising candidates. However, in light of the currently available multi-epoch SPHERE data, only the candidate around Smethells 20 remains a strong target for follow-up.

Context . The wide cavity in the PDS 70 protoplanetary disk harbors two directly imaged confirmed protoplanets. Several studies have proposed the existence of a third inner planet candidate at ~13 au, labeled as PDS 70 d. While its motion is consistent with a Keplerian orbit, its unusually blue spectrum challenges a planetary interpretation. Aims . We investigated the presence and nature of a third inner planet using new SPHERE and GRAVITY observations. Methods . Using the star-hopping strategy, we obtained new coronagraphic SPHERE/IRDIS observations of PDS 70 in dual-polarization imaging mode in the H band, as well as non-coronagraphic observations with SPHERE/IRDIFS covering the YJHK bands. We also searched for a planetary-like signal using GRAVITY+ in astrometric mode with the four-unit-telescope configuration. Results . We consistently detect two inner emission features with SPHERE: one corresponding to the previously proposed planet candidate at ~13 au and another that appears to share the same orbit but leads it by ~120° (clockwise) with a more elongated morphology. Both features exhibit dust-scattered light spectra while displaying different colors, which may indicate differences in dust grain sizes. We show that such a configuration is consistent with co-orbital dust accumulated at the stable Lagrangian regions of a yet undetected planet, distinct from the previously proposed candidate. The analysis of GRAVITY data at the predicted position of this newly proposed planet has resulted in a marginal (3 σ ) detection located between the two clumps along the same orbit ( ρ = 76.2 ± 0.29 mas, and position angle PA = 226.50 ± 0.21°), and consistent with a ~3 M _Jup planet. This planet-like signal aligns with a narrow shadow detected in the outer disk with SPHERE. Additionally, with SPHERE we detect polarized emission very close to the star, which likely arise from the inner disk, with an inclination of 50° and a PA of ~135°. The fact that the two dust clumps appear embedded within this polarized emission motivates an inner disk-related alternative scenario. Conclusions . We conclude that the emission from the previously reported third planet candidate could arise either from a dust clump trailing a yet undetected planet along the same orbit, or from a rotating substructure within the inner disk. Additional observations are required to further test these two proposed scenarios. In particular, confirming the new GRAVITY planet-like signal would support the use of co-orbital substructures as indirect tracers of embedded planets.

We report the direct imaging discovery of a third exoplanet in the β Pictoris ( β Pic) system. We detect β Pictoris d ( β Pic d) in noncoronagraphic observations obtained with the Very Large Telescope (VLT) Enhanced Resolution Imager and Spectrograph (ERIS), as well as multi-epoch archival datasets from the JWST Near Infrared Camera (NIRCam) and VLT/SPHERE. Astrometric measurements over an 11 yr baseline demonstrate that it is consistent with a gravitationally bound source with orbital motion. Joint multi-planet orbit fits of all three planets in the system yield a semimajor axis of 26 . 0 − 6.1 + 2.2 au and inclination 89 . 0 − 0.6 + 0.7 deg for planet d. β Pic d has a larger orbital semimajor axis than the other known planets in the system, but is coplanar with the inner two planets, and its orbit is consistent with sculpting the inner edge of the debris disk. β Pic d has a contrast of Δ L ′ = 12.11 ± 0.15 mag, with colors and luminosity that closely match those of 51 Eri b, another exoplanet in the β Pic moving group. Its VLT/ERIS and JWST/NIRCam colors are distinct from those of free-floating planetary-mass objects of a similar age and temperature. Its red F410M − F444W color indicates strong CO ₂ absorption in its atmosphere and suggests significant enhancement in metals compared to free-floating objects. From the ATMO hot-start evolutionary models, we estimate an effective temperature of 60 0 − 60 + 45 K and mass of 2.4 ± 0.6 M _Jup , which also closely matches similar estimates for 51 Eri b. β Pic d is among the lowest-mass exoplanets imaged from the ground. This discovery highlights the deep sensitivity achievable with ground-based imaging in the mid-infrared and the discovery potential of future high-contrast observations with the Extremely Large Telescope.

Context . Silicates are key constituents of planet-forming disks and are among the most important building blocks of rocky planets. Mid-infrared spectral features of micron-sized silicate grains are powerful tracers of grain growth, mineralogy, and disk chemistry. Aims . We characterized the dust mineralogy in T Tauri disks using James Webb Space Telescope (JWST)/Mid-Infrared Instrument (MIRI) observations. A further aim of ours was to investigate the connections between the dust and molecular gas compositions. Methods . We analyzed JWST/MIRI spectra of 26 disks as part of the MIRI mid-Infrared Disk Survey (MINDS). We employed spectral decomposition with our new DustComp tool to derive the mass fractions of individual dust species. We included in our fits Mg ₂ SiO ₄ (forsterite), MgSiO ₃ (enstatite), and SiO ₂ (silica) together with amorphous silicates of corresponding stoichiometry. Results . We find that Mg-rich (and Fe-poor) silicates represent our data well. Fit residuals are typically within ±3%. Grain size distributions are skewed toward larger sizes (>2 μm), indicating significant growth. Large (~5 μm-sized) amorphous Mg-silicates were robustly detected, whereas the presence of large crystalline grains could not be firmly established. The average dust composition is dominated by grains of Mg ₂ SiO ₄ stoichiometry (~60%, including amorphous and crystalline state), followed by MgSiO ₃ (~30%) and SiO ₂ (∼10%). The mass fractions of crystalline grains are typically in the 5-24% range, with a mean of 14%. We robustly detected annealed silica in nine objects, with cristobalite as the main polymorph. We found a correlation between dust and molecular gas composition: disks with strong annealed silica features show relatively strong CO ₂ emission, while forsterite-rich disks display stronger H ₂ O emission. Disks with annealed silica features may also have elevated gas-phase C/O ratios, suggesting a process, such as dust sublimation and recondensation, that establishes thermo-chemical equilibrium between solids and gas. Conclusions . The correlation between dust and gas may provide the first indication that the molecular gas composition regulates the availability of dust species in the inner disk.

Hot exozodiacal dust has been detected in approximately 20% of nearby main-sequence stars, indicating that it is a common feature in extrasolar planetary systems. However, their spatial distribution and grain properties remain poorly understood. We aim to show that the spatial distribution of hot dust around β Pictoris -- an iconic planetary system with two known planets and a population of exocomets -- can be effectively constrained through a detailed analysis of optical long-baseline interferometry data. We obtained -band (łambda ∼ 3.5 μm) observations of β Pictoris with the MATISSE instrument at the VLTI. We first developed a method to assess correlations in the visibility measurements by estimating the full data covariance matrix. We then modeled the circumstellar emission using geometric brightness distributions to fit the observed visibilities. L This study reveals circumstellar emission around β Pictoris consistent with hot exozodiacal dust. By modeling the emission both accounting and not accounting for correlations in the data, we demonstrate their significant impact on the inferred dust properties. The best-fit model reveals a compact (∼0.05 au), highly inclined dust structure near the sublimation radius, misaligned by ∼ 60 dust component near 1 au. on the sky plane with respect to the extended edge-on outer disk, contributing ∼ 4%–7.5% of the total flux at łambda = 3.4 μm, and is composed of submicron-sized grains. The data are also compatible with an additional In the case of β Pictoris, the two-decade-old paradigm -- placing hot exozodiacal dust near the sublimation radius and composed of submicron-sized grains -- finds observational support in the detailed analysis of MATISSE data. The misalignment with the known debris disk further supports a link to the exocometary activity.

Context . The James Webb Space Telescope (JWST) provides low- to medium-resolution spectra with unprecedented precision and broad near- to mid-infrared wavelength coverage, thus enabling the detailed characterization of exoplanet atmospheres. Given the complexity of JWST data and the diversity of observing modes, it is essential to understand the information content of the resulting spectra to optimize observation strategies and assess the limits of atmospheric inference. Aims . This work presents a new JWST NIRISS SOSS transit observation of the warm sub-Saturn HAT-P-12b. Together with complementary NIRSpec G395M and MIRI LRS data, this enables a detailed assessment of the information content across JWST instruments over the full accessible wavelength range (excluding MIRI MRS). Methods . The NIRISS data were reduced, and the impact of specific reduction choices on the resulting transmission spectrum was assessed. Atmospheric retrievals were performed for all combinations of JWST data, supplemented by archival HST observations in select cases. The analysis further included evaluations of molecular detection significances and assumptions about the atmospheric structure. Results . The same four molecules previously reported are significantly detected: H ₂ O, CO ₂ , CO, and H ₂ S. Except for H ₂ O, all require NIRSpec coverage for detection, while H ₂ S is only detected in multi-instrument retrievals. Abundance constraints obtained using HST WFC3 instead of JWST NIRISS SOSS are largely consistent, particularly when combining instruments, but NIRISS SOSS proved essential to establishing robust evidence for nongray cloud behavior. A moderately steep scattering slope ( p < 4) is consistently retrieved across different HST STIS reductions. Conclusions . Single-instrument retrievals, even when yielding significant detections, tend to overestimate molecular abundances. In contrast, retrievals that combine spectra from multiple JWST instruments generally converge toward consistent abundance constraints. The derived C/O ratio remains sensitive to subtle differences between NIRSpec reductions, owing to the instrument’s exclusive coverage of the carbon-bearing molecules CO ₂ and CO, so its interpretation requires caution. The results are broadly consistent with information content studies of the benchmark target WASP-39b, although differences, including the absence of a preference for non-isothermal T-P profiles, highlight variations in information content across exoplanet types.

The HD 135344B (SAO 206462) disk exhibits strong signposts of planet formation both in scattered light and submillimeter continuum images. ALMA images in the submillimeter revealed a gap-crossing dust filament whose position coincides with a twist detected in the scattered-light spiral structure. Analysis of the spiral dynamics in polarized light also hints at a spiral-driving protoplanet in the submillimeter gap. We aim to study the overall dynamics of the three spirals in the disk, as well as the motion of the twist over a 10-year baseline, at different IR wavelengths. We also seek to assess the authenticity of a candidate protoplanet recently claimed in the disk. We used high-fidelity postprocessing algorithms such as iterative principal component analysis to minimize the biases induced by angular differential imaging on extended sources and conduct a thorough analysis of archival VLT/NACO, VLT/SPHERE, VLT/ERIS datasets in order to obtain the spiral traces and measure their orbital motion in multiple wavelength bands in scattered light. and We also reprocessed archival JWST/NIRCam datasets with these algorithms. We measured an average spiral orbital motion of 0fdg81 ± 0fdg05 yr -1 $ , in agreement with the literature value of about 0 at all wavelengths. With simple modeling of the twist morphology, we confirm that it is indeed co-moving with the spiral in which it is embedded. While the position angle of the twist coincides with the dust filament, it is located at a smaller angular separation from the star, which we attribute to the fact that the spiral trace moves away from the central star with increasing wavelength. We find that a previously claimed protoplanet candidate in the disk can be adequately explained as a postprocessing artifact. -1 Our confirmation that the motion of the scattered light twist is consistent with the orbital velocity of a planet at 69± 4 au over a 10-year baseline suggests that the spirals, the gap, and the dust filament in the submillimeter continuum, as well as the twist in scattered light, could indeed all be attributed to the same hypothetical protoplanet deeply embedded within the spiral. A perplexing trend for a wavelength-dependence of the angular distance of the spiral traces to the central star still remains to be explained.

Context . The direct imaging of potentially habitable exoplanets is one prime science case for high-contrast imaging (HCI) instruments on ground-based, extremely large telescopes. Most such exoplanets orbit close to their host stars, where their observation is limited by fast-moving atmospheric speckles and quasi-static noncommon path aberrations (NCPA). Aims . Conventional NCPA correction methods often use mechanical mirror probes, which compromise performance during operation. This work presents machine-learning-based NCPA control methods that automatically detect and correct both dynamic and static NCPA errors by leveraging past telemetry data and sequential phase diversity. Methods . We extend previous work in reinforcement learning (RL) for adaptive optics (AO) to focal plane wavefront control. A new model-based RL algorithm, Policy Optimization for Noncommon Path Aberrations (PO4NCPA), interprets the focal plane image as input data and, through sequential phase diversity, determines phase corrections that optimize both non-coronagraphic and post-coronagraphic point spread functions (PSFs) without prior system knowledge. Furthermore, we demonstrate the effectiveness of this approach by numerically simulating static NCPA errors on a ground-based telescope and an infrared imager affected by water vapor-induced seeing (dynamic NCPAs). Results . Simulations show that PO4NCPA robustly compensates static and dynamic NCPAs. In static cases, it achieves near-optimal focal plane light suppression with a coronagraph and near-optimal Strehl without one. With dynamic NCPA, it matches the performance of the modal least-squares reconstruction combined with a 1-step delay integrator in these metrics, though with a higher wavefront root mean square error (RMSE), especially for high-order modes. The method remains effective for the Extremely Large Telescope (ELT) pupil, the vector vortex coronagraph, under photon and background noise. Conclusions . PO4NCPA is model-free and can be directly applied to standard imaging as well as to any type of coronagraphy; its submillisecond inference times and performance also make it suitable for real-time low-order correction of atmospheric turbulence beyond HCI requirements.

Aims . We describe the design, laboratory manufacture, and on-sky testing of the grating vector apodizing phase plate (gvAPP) coronagraph for the Enhanced Resolution Imager and Spectrograph (ERIS) on the Very Large Telescope. Methods . We used both laboratory measurements and on-sky observations to characterise the gvAPP in several different filters, from the K to the L band. Results . In testing, the gvAPP reaches its design specification in the transmission of the optic with 90% in the K bands and 60% in the L band. While the gvAPP reaches its designed raw contrast performance of 1 × 10 ⁻⁵ , it does not reach the post-processed contrast of 5 × 10 ⁻⁵ in on-sky observations. Electronic detector noise, due to the Airy core of the coronagraphic point spread function inducing cross-talk between the readout amplifiers, produces a repeated pattern within the coronagraphic regions of the gvAPP. Conclusions . Despite these limitations, we recommend the gvAPP as a tool for characterising substellar companions with known separations and position angles, which allow them to be placed in the coronagraphic dark holes for observations. The ERIS gvAPP’s leakage term can also be used as a photometric reference for time series observations; however, we caution that the contrast performance may limit such studies to only the brightest targets. ERIS gvAPP data quality may be improved further with better modelling of detector electronic noise. This work is a pathfinder for Extremely Large Telescope instruments including METIS, which will include gvAPP coronagraphs with improved designs based on these results.

Context . Exocomets are small bodies that evaporate when they approach their host star. They can be detected based on the variability of non-photospheric features using spectroscopy and/or asymmetric transits in time-series photometry. Over the past four decades, about 30 systems have exhibited such variations and have therefore been classified as exocomet host stars. However, some recent publications have pointed out mechanisms that might mimic exocometary features. Therefore, careful monitoring is needed to confirm the origin of the observed variability. Aims . In this paper, we aim to investigate the exocomet nature of the non-photospheric variable features observed in the exocomet candidate stars HD 36546, HD 42111, and HD 85905. All of them have shown some degree of variability, particularly in their Ca II K line. Methods . We analysed the non-photospheric Ca II K line features from high-resolution spectra obtained using new NOT/FIES and Mercator/HERMES, along with some additional archival spectra of the target stars. The variability was quantified through the changes in the equivalent widths of those features, which are assumed to be of circumstellar origin. The column densities were also estimated for each variable feature. Results . Strong variability was found for HD 85905, consistent with a potential link to exocometary activity. However, the binarity of the system, which we confirmed through interferometric VLTI/PIONIER observations, complicates the interpretation of these signatures and prevents us from drawing definitive conclusions. The remaining two sources do not show any significant variability, but due to the sporadic nature of the exocometary events, we cannot discard the exocomet hypothesis. Further monitoring of the stars will be necessary to carry out a robust determination of the variability patterns and timescales that would completely rule out other scenarios.