The beta Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR

[abridged] We analyzed mid-infrared high-contrast coronagraphic images of the beta Pictoris system, taking advantage of the NEAR experiment using the VLT/VISIR instrument. The goal of our analysis is to investigate both the detection of the planet beta Pictoris b and of the disk features at mid-IR wavelengths. In addition, by combining several epochs of observation, we expect to constrain the position of the known clumps and improve our knowledge on the dynamics of the disk. To evaluate the planet b flux contribution, we extracted the photometry and compared it to the flux published in the literature. In addition, we used previous data from T-ReCS and VISIR, to study the evolution of the position of the southwest clump that was initially observed in the planetary disk back in 2003. While we did not detect the planet b, we were able to put constraints on the presence of circumplanetary material, ruling out the equivalent of a Saturn-like planetary ring around the planet. The disk presents several noticeable structures, including the known southwest clump. Using a 16-year baseline, sampled with five epochs of observations, we were able to examine the evolution of the clump: the clump orbits in a Keplerian motion with an sma of 56.1+-0.4 au. In addition to the known clump, the images clearly show the presence of a second clump on the northeast side of the disk and fainter and closer structures that are yet to be confirmed. We found correlations between the CO clumps detected with ALMA and the mid-IR images. If the circumplanetary material were located at the Roche radius, the maximum amount of dust determined from the flux upper limit around beta Pictoris b would correspond to the mass of an asteroid of 5 km in diameter. Finally, the Keplerian motion of the southwestern clump is possibly indicative of a yet-to-be-detected planet or signals the presence of a vortex.Comment: Accepted in Astronomy and Astrophysic

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.Comment: 32 pages, 16 figures, 6 tables, 2 appendice

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 1256–1257 b

The unprecedented medium-resolution (R λ ∼ 1500–3500) near- and mid-infrared (1–18 μm) spectrum provided by JWST for the young (140 ± 20 Myr) low-mass (12–20 MJup) L–T transition (L7) companion VHS 1256 b gives access to a catalog of molecular absorptions. In this study, we present a comprehensive analysis of this data set utilizing a forward-modeling 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, γ, f sed, 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 VHS 1256 b, 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 VHS 1256 b 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

Caractérisation des exoplanètes gazeuses géantes avec l’instrument en infrarouge moyen MIRI du JWST

The study of exoplanet atmospheres is an important topic for today's scientific community, but the new space telescope, the James Webb Space Telescope (JWST), is expected to provide a major breakthrough in our understanding of exosystems. Imaging exoplanets remains a real challenge, as it requires very high contrast at very small angular separations. However, with the current generation of instruments on ground-based telescopes, it is possible to image young, and therefore hot, long-period giant planets at near-infrared wavelengths. The atmospheres of these planets can be characterized using photometry, as well as low- and medium-resolution spectra. Nevertheless, these observations are limited to the near-IR. JWST's mid-IR instrument MIRI opens up a new observation window with unprecedented sensitivity. At these wavelengths, the contrast is favorable for detecting the emission of young and giant exoplanets, and many molecules become accessible. Moreover, the wide spectral range makes it possible to better constrain many exoplanet properties. Two MIRI observation modes are relevant to exoplanet imaging characterization : the medium-resolution spectro-imager (MRS) and the coronagraphs. The MRS is an integral-field spectrometer covering wavelengths from 5 to 28 microns, with resolution up to 3700. This mode had not been developed for high-contrast imaging, but a recent method is proven to be promising for disentangling stellar from planetary signals with this type of instrument : the molecular mapping. The first part of my thesis focuses on predicting the performance of the MRS to characterize exoplanets using simulated data. Many molecules can be detected, depending on the temperature and brightness of the target observed. We have simulated several systems detected in direct imaging to prepare for future JWST observing programs, and to explore the sensitivity of the method for determining atmospheric parameters. Once the telescope was operational, in the summer of 2022, planetary masses companions have been observed with the MRS. The application of molecular mapping to these first data acquired by JWST validates the performance obtained with simulations, and highlights the challenges of the method. The second part of my thesis presents coronagraphic observations of planetary systems with MIRI : the HR 8799 system and, in more detail, the HD 95086 system. Mid-IR observations differ from near-IR results, and the usual analysis methods are adapted. This enables us to characterize the atmospheres of giant planets by removing the degeneracies revealed by near-IR observations. The MRS and the coronagraphs are complementary and provide crucial information for understanding the phenomena at play in the atmospheres of the young planets imaged. This leads us to a better comprehension of the mechanisms of formation and evolution of planetary systems, and thus of our own Solar System.L'étude des atmosphères d'exoplanètes est un enjeu important pour la communauté scientifique actuelle, mais le nouveau télescope spatial, le James Webb Space Telescope (JWST), promet une avancée majeure dans la compréhension des exosystèmes. L’imagerie des exoplanètes reste un réel défi : cela nécessite d’atteindre des très hauts contrastes à de très petites séparations angulaires. Avec la génération actuelle d’instruments sur les télescopes au sol, il est toutefois possible d'imager en infrarouge proche des planètes géantes, jeunes, et donc chaudes, à longues périodes. L'atmosphère de ces planètes peut être caractérisée à partir de leur photométrie, mais aussi grâce à des spectres à basse, voir moyenne résolution. Néanmoins, ces observations sont limitées à l’IR proche. L’instrument en IR moyen MIRI du JWST donne ainsi accès à une nouvelle fenêtre d’observation avec une sensibilité inégalée. À ces longueurs d’onde, le contraste est favorable pour détecter l’émission des exoplanètes jeunes et géantes, et de nombreuses molécules deviennent accessibles. De plus, l’étendue du domaine spectrale est très favorable pour mieux contraindre de nombreuses propriétés des exoplanètes. Deux modes d’observations de MIRI sont pertinents pour la caractérisation des exoplanètes en imagerie : le spectro-imageur à moyenne résolution, le MRS, et les coronographes. Le MRS est un spectromètre à champ intégral couvrant les longueurs d’onde de 5 à 28 microns avec une résolution jusqu’à 3700. Ce mode n’avait pas été développé pour l’imagerie haut contraste. Néanmoins, une méthode récente s’avère prometteuse pour distinguer le signal stellaire du signal planétaire avec ce type d'instruments : le molecular mapping. La première partie de mon travail de thèse se concentre sur les prédictions des performances du MRS pour caractériser des exoplanètes à partir de données simulées. De nombreuses molécules peuvent être détectées selon la température et la luminosité de la cible observée. Nous avons simulé plusieurs systèmes détectés en imagerie afin de préparer des futurs programmes d'observations du JWST et d'explorer la sensibilité de la méthode pour déterminer les paramètres atmosphériques. Une fois le télescope opérationnel, au cours de l’été 2022, des compagnons de masses planétaires ont été observées avec le MRS. L’application du molecular mapping à ces premières données acquise par le JWST valide les performances obtenues avec les simulations, et met en évidence des enjeux de la méthode. La seconde partie de ma thèse présente les observations coronographiques des systèmes planétaires avec MIRI : le système HR 8799 et plus en détail le système HD 95086. Les observations en IR moyen diffèrent des résultats en IR proche, et les méthodes usuelles d’analyse sont adaptées. Ainsi, il est possible de caractériser les atmosphères des planètes géantes en levant des dégénérescences mises en évidence avec les observations en IR proche. Le MRS et les coronographes sont complémentaires et apportent des informations cruciales pour comprendre les phénomènes en jeu dans les atmosphères des planètes jeunes imagées. Cela nous mène à mieux comprendre les mécanismes de formations et d’évolution des systèmes planétaires, et ainsi de notre propre Système Solaire

Caractérisation des exoplanètes gazeuses géantes avec l’instrument en infrarouge moyen MIRI du JWST

The study of exoplanet atmospheres is an important topic for today's scientific community, but the new space telescope, the James Webb Space Telescope (JWST), is expected to provide a major breakthrough in our understanding of exosystems. Imaging exoplanets remains a real challenge, as it requires very high contrast at very small angular separations. However, with the current generation of instruments on ground-based telescopes, it is possible to image young, and therefore hot, long-period giant planets at near-infrared wavelengths. The atmospheres of these planets can be characterized using photometry, as well as low- and medium-resolution spectra. Nevertheless, these observations are limited to the near-IR. JWST's mid-IR instrument MIRI opens up a new observation window with unprecedented sensitivity. At these wavelengths, the contrast is favorable for detecting the emission of young and giant exoplanets, and many molecules become accessible. Moreover, the wide spectral range makes it possible to better constrain many exoplanet properties. Two MIRI observation modes are relevant to exoplanet imaging characterization : the medium-resolution spectro-imager (MRS) and the coronagraphs. The MRS is an integral-field spectrometer covering wavelengths from 5 to 28 microns, with resolution up to 3700. This mode had not been developed for high-contrast imaging, but a recent method is proven to be promising for disentangling stellar from planetary signals with this type of instrument : the molecular mapping. The first part of my thesis focuses on predicting the performance of the MRS to characterize exoplanets using simulated data. Many molecules can be detected, depending on the temperature and brightness of the target observed. We have simulated several systems detected in direct imaging to prepare for future JWST observing programs, and to explore the sensitivity of the method for determining atmospheric parameters. Once the telescope was operational, in the summer of 2022, planetary masses companions have been observed with the MRS. The application of molecular mapping to these first data acquired by JWST validates the performance obtained with simulations, and highlights the challenges of the method. The second part of my thesis presents coronagraphic observations of planetary systems with MIRI : the HR 8799 system and, in more detail, the HD 95086 system. Mid-IR observations differ from near-IR results, and the usual analysis methods are adapted. This enables us to characterize the atmospheres of giant planets by removing the degeneracies revealed by near-IR observations. The MRS and the coronagraphs are complementary and provide crucial information for understanding the phenomena at play in the atmospheres of the young planets imaged. This leads us to a better comprehension of the mechanisms of formation and evolution of planetary systems, and thus of our own Solar System.L'étude des atmosphères d'exoplanètes est un enjeu important pour la communauté scientifique actuelle, mais le nouveau télescope spatial, le James Webb Space Telescope (JWST), promet une avancée majeure dans la compréhension des exosystèmes. L’imagerie des exoplanètes reste un réel défi : cela nécessite d’atteindre des très hauts contrastes à de très petites séparations angulaires. Avec la génération actuelle d’instruments sur les télescopes au sol, il est toutefois possible d'imager en infrarouge proche des planètes géantes, jeunes, et donc chaudes, à longues périodes. L'atmosphère de ces planètes peut être caractérisée à partir de leur photométrie, mais aussi grâce à des spectres à basse, voir moyenne résolution. Néanmoins, ces observations sont limitées à l’IR proche. L’instrument en IR moyen MIRI du JWST donne ainsi accès à une nouvelle fenêtre d’observation avec une sensibilité inégalée. À ces longueurs d’onde, le contraste est favorable pour détecter l’émission des exoplanètes jeunes et géantes, et de nombreuses molécules deviennent accessibles. De plus, l’étendue du domaine spectrale est très favorable pour mieux contraindre de nombreuses propriétés des exoplanètes. Deux modes d’observations de MIRI sont pertinents pour la caractérisation des exoplanètes en imagerie : le spectro-imageur à moyenne résolution, le MRS, et les coronographes. Le MRS est un spectromètre à champ intégral couvrant les longueurs d’onde de 5 à 28 microns avec une résolution jusqu’à 3700. Ce mode n’avait pas été développé pour l’imagerie haut contraste. Néanmoins, une méthode récente s’avère prometteuse pour distinguer le signal stellaire du signal planétaire avec ce type d'instruments : le molecular mapping. La première partie de mon travail de thèse se concentre sur les prédictions des performances du MRS pour caractériser des exoplanètes à partir de données simulées. De nombreuses molécules peuvent être détectées selon la température et la luminosité de la cible observée. Nous avons simulé plusieurs systèmes détectés en imagerie afin de préparer des futurs programmes d'observations du JWST et d'explorer la sensibilité de la méthode pour déterminer les paramètres atmosphériques. Une fois le télescope opérationnel, au cours de l’été 2022, des compagnons de masses planétaires ont été observées avec le MRS. L’application du molecular mapping à ces premières données acquise par le JWST valide les performances obtenues avec les simulations, et met en évidence des enjeux de la méthode. La seconde partie de ma thèse présente les observations coronographiques des systèmes planétaires avec MIRI : le système HR 8799 et plus en détail le système HD 95086. Les observations en IR moyen diffèrent des résultats en IR proche, et les méthodes usuelles d’analyse sont adaptées. Ainsi, il est possible de caractériser les atmosphères des planètes géantes en levant des dégénérescences mises en évidence avec les observations en IR proche. Le MRS et les coronographes sont complémentaires et apportent des informations cruciales pour comprendre les phénomènes en jeu dans les atmosphères des planètes jeunes imagées. Cela nous mène à mieux comprendre les mécanismes de formations et d’évolution des systèmes planétaires, et ainsi de notre propre Système Solaire

Caractérisation des exoplanètes gazeuses géantes avec l’instrument en infrarouge moyen MIRI du JWST

The study of exoplanet atmospheres is an important topic for today's scientific community, but the new space telescope, the James Webb Space Telescope (JWST), is expected to provide a major breakthrough in our understanding of exosystems. Imaging exoplanets remains a real challenge, as it requires very high contrast at very small angular separations. However, with the current generation of instruments on ground-based telescopes, it is possible to image young, and therefore hot, long-period giant planets at near-infrared wavelengths. The atmospheres of these planets can be characterized using photometry, as well as low- and medium-resolution spectra. Nevertheless, these observations are limited to the near-IR. JWST's mid-IR instrument MIRI opens up a new observation window with unprecedented sensitivity. At these wavelengths, the contrast is favorable for detecting the emission of young and giant exoplanets, and many molecules become accessible. Moreover, the wide spectral range makes it possible to better constrain many exoplanet properties. Two MIRI observation modes are relevant to exoplanet imaging characterization : the medium-resolution spectro-imager (MRS) and the coronagraphs. The MRS is an integral-field spectrometer covering wavelengths from 5 to 28 microns, with resolution up to 3700. This mode had not been developed for high-contrast imaging, but a recent method is proven to be promising for disentangling stellar from planetary signals with this type of instrument : the molecular mapping. The first part of my thesis focuses on predicting the performance of the MRS to characterize exoplanets using simulated data. Many molecules can be detected, depending on the temperature and brightness of the target observed. We have simulated several systems detected in direct imaging to prepare for future JWST observing programs, and to explore the sensitivity of the method for determining atmospheric parameters. Once the telescope was operational, in the summer of 2022, planetary masses companions have been observed with the MRS. The application of molecular mapping to these first data acquired by JWST validates the performance obtained with simulations, and highlights the challenges of the method. The second part of my thesis presents coronagraphic observations of planetary systems with MIRI : the HR 8799 system and, in more detail, the HD 95086 system. Mid-IR observations differ from near-IR results, and the usual analysis methods are adapted. This enables us to characterize the atmospheres of giant planets by removing the degeneracies revealed by near-IR observations. The MRS and the coronagraphs are complementary and provide crucial information for understanding the phenomena at play in the atmospheres of the young planets imaged. This leads us to a better comprehension of the mechanisms of formation and evolution of planetary systems, and thus of our own Solar System.L'étude des atmosphères d'exoplanètes est un enjeu important pour la communauté scientifique actuelle, mais le nouveau télescope spatial, le James Webb Space Telescope (JWST), promet une avancée majeure dans la compréhension des exosystèmes. L’imagerie des exoplanètes reste un réel défi : cela nécessite d’atteindre des très hauts contrastes à de très petites séparations angulaires. Avec la génération actuelle d’instruments sur les télescopes au sol, il est toutefois possible d'imager en infrarouge proche des planètes géantes, jeunes, et donc chaudes, à longues périodes. L'atmosphère de ces planètes peut être caractérisée à partir de leur photométrie, mais aussi grâce à des spectres à basse, voir moyenne résolution. Néanmoins, ces observations sont limitées à l’IR proche. L’instrument en IR moyen MIRI du JWST donne ainsi accès à une nouvelle fenêtre d’observation avec une sensibilité inégalée. À ces longueurs d’onde, le contraste est favorable pour détecter l’émission des exoplanètes jeunes et géantes, et de nombreuses molécules deviennent accessibles. De plus, l’étendue du domaine spectrale est très favorable pour mieux contraindre de nombreuses propriétés des exoplanètes. Deux modes d’observations de MIRI sont pertinents pour la caractérisation des exoplanètes en imagerie : le spectro-imageur à moyenne résolution, le MRS, et les coronographes. Le MRS est un spectromètre à champ intégral couvrant les longueurs d’onde de 5 à 28 microns avec une résolution jusqu’à 3700. Ce mode n’avait pas été développé pour l’imagerie haut contraste. Néanmoins, une méthode récente s’avère prometteuse pour distinguer le signal stellaire du signal planétaire avec ce type d'instruments : le molecular mapping. La première partie de mon travail de thèse se concentre sur les prédictions des performances du MRS pour caractériser des exoplanètes à partir de données simulées. De nombreuses molécules peuvent être détectées selon la température et la luminosité de la cible observée. Nous avons simulé plusieurs systèmes détectés en imagerie afin de préparer des futurs programmes d'observations du JWST et d'explorer la sensibilité de la méthode pour déterminer les paramètres atmosphériques. Une fois le télescope opérationnel, au cours de l’été 2022, des compagnons de masses planétaires ont été observées avec le MRS. L’application du molecular mapping à ces premières données acquise par le JWST valide les performances obtenues avec les simulations, et met en évidence des enjeux de la méthode. La seconde partie de ma thèse présente les observations coronographiques des systèmes planétaires avec MIRI : le système HR 8799 et plus en détail le système HD 95086. Les observations en IR moyen diffèrent des résultats en IR proche, et les méthodes usuelles d’analyse sont adaptées. Ainsi, il est possible de caractériser les atmosphères des planètes géantes en levant des dégénérescences mises en évidence avec les observations en IR proche. Le MRS et les coronographes sont complémentaires et apportent des informations cruciales pour comprendre les phénomènes en jeu dans les atmosphères des planètes jeunes imagées. Cela nous mène à mieux comprendre les mécanismes de formations et d’évolution des systèmes planétaires, et ainsi de notre propre Système Solaire

Serendipitous observation of a white dwarf companion to a <i>JWST</i>/MIRI coronagraphic calibrator

International audienceWe present the unplanned detection of a white dwarf companion to the star HD 218261 in mid-infrared (10-16 μm) observations with JWST /MIRI. This star was observed as a calibrator for coronagraphic observations of the exoplanet host HR 8799. HD 218261 B has only previously been detected by Gaia , and only in visible light. We confidently detect the companion in the midinfrared, where it is less luminous than the primary by a factor of ∼104. The visible and mid-infrared photometry are consistent with a white dwarf of Teff ≈ 10000 K, M ≈ 0 . 8 M$_{\odot}$ , though observation of its optical spectrum is required to precisely constrain its physical parameters. These results demonstrate that precise mid-infrared photometry of white dwarf companions to bright stars can be obtained with MIRI, opening up new possibilities for studying white dwarfs in close binaries

First unambiguous detection of ammonia in the atmosphere of a planetary mass companion with JWST/MIRI coronagraphs

Context. The newly accessible mid-infrared (MIR) window offered by the James Webb Space Telescope (JWST) for exoplanet imaging is expected to provide valuable information to characterize their atmospheres. In particular, coronagraphs on board the JWST Mid-InfraRed instrument (MIRI) are capable of imaging the coldest directly imaged giant planets at the wavelengths where they emit most of their flux. The MIRI coronagraphs have been specially designed to detect the NH3 absorption around 10.5 mu m, which has been predicted by atmospheric models and should be detectable for planets colder than 1200 K. Aims. We aim to assess the presence of NH3 while refining the atmospheric parameters of one of the coldest companions detected by directly imaging GJ 504 b. Its mass is still a matter of debate and depending on the host star age estimate, the companion could either be placed in the brown dwarf regime of similar to 20 M-Jup or in the young Jovian planet regime of similar to 4 M-Jup. Methods. We present an analysis of new MIRI observations, using the coronagraphic filters F1065C, F1140C, and F1550C of the GJ 504 system. We took advantage of previous observations of reference stars to build a library of images and to perform a more efficient subtraction of the stellar diffraction pattern. We used an atmospheric grid from the Exo-REM model to refine the atmospheric parameters by combining archival near-infrared (NIR) photometry with the MIR photometry. Results. We detected the presence of NH3 at 12.5 sigma and measured its volume mixing ratio of 10(-5.3 +/- 0.07) in the atmosphere of GJ 504 b. These results are in line with atmospheric model expectations for a planetary-mass object and observed in brown dwarfs within a similar temperature range. The best-fit model with Exo-REM provides updated values of its atmospheric parameters, yielding a temperature of T-eff = 512 +/- 10 K and radius of R = 1.08(-0.03)(+0.04) R-Jup. Conclusions. These observations demonstrate the capability of MIRI coronagraphs to detect NH3 and to provide the first MIR observations of one of the coldest directly imaged companions. Overall, NH3 is a key molecule for characterizing the atmospheres of cold planets, offering valuable insights into their surface gravity. These observations provide valuable information for future spectroscopic observations planned with JWST, in particular, with the MIRI medium-resolution spectrometer (MRS), which will allow us to characterize the atmosphere of GJ 504 b in depth.ISSN:0004-6361ISSN:1432-074

Imaging detection of the inner dust belt and the four exoplanets in the HR 8799 system with JWST s MIRI coronagraph

Context. The MIRI instrument on board JWST is now offering high-contrast imaging capacity at mid-IR wavelengths, thereby opening a completely new field of investigation for characterizing young exoplanetary systems. Aims. The multiplanet system HR 8799 is the first target observed with MIRIa s coronagraph as part of the MIRI-EC Guaranteed Time Observations (GTO) exoplanet program, launched in November 2022. We obtained deep observations in three coronagraphic filters, from a10 to 15 μm (F1065C, F1140C, F1550C), and one standard imaging filter at a20 μm (F2100W). The goal of this work is to extract photometry for the four planets and to detect and investigate the distribution of circumstellar dust. Methods. Using dedicated observations of a reference star, we tested several algorithms to subtract the stellar diffraction pattern, while preserving the fluxes of planets, which can be significantly affected by over-subtraction. To obtain correct measurements of the planeta s flux values, the attenuation by the coronagraphs as a function of their position must be accounted for, as well as an estimation of the normalisation with respect to the central star. We tested several procedures to derive averaged photometric values and error bars. Results. These observations have enabled us to obtain two main results. First, the four planets in the system are well recovered and we were able to compare their mid-IR fluxes, combined with near-IR flux values from the literature, to two exoplanet atmosphere models: ATMO and Exo-REM. As a main outcome, the MIRI photometric data points imply larger radii (1.04 or 1.17 RJ for planet b) and cooler temperatures (950 or 1000 K for planet b), especially for planet b, in better agreement with evolutionary models. Second, these JWST/MIRI coronagraphic data also deliver the first spatially resolved detection of the inner warm debris disk, the radius of which is constrained to about 15 au, with flux densities that are comparable to (but lower than) former unresolved spectroscopic measurements with Spitzer. Conclusions. The coronagraphs coming from MIRI ushers in a new vision of known exoplanetary systems that differs significantly from shorter wavelength, high-contrast images delivered by extreme adaptive optics from the ground. Inner dust belts and background galaxies become dominant at some mid-IR wavelengths, potentially causing confusion in detecting exoplanets. Future observing strategies and data reductions ought to take such features into account.ISSN:0004-6361ISSN:1432-074

MIRI-JWST mid-infrared direct imaging of the debris disk of HD 106906: Structure and mass of the disk

International audienceContext. We report MIRI-JWST coronagraphic observations at 11.3 and 15.5 μm of the debris disk around the young star HD 106906. The wavelength range is sensitive to the thermal emission of the dust heated by the central star.Aims. The observations were made to characterize the structure of the disk through the thermal emission, to search for clues to the presence of a central void of dust particles, and to derive the mass of the dust and the temperature distribution. Another goal was also to constrain the size distribution of the grains.Methods. The data were reduced and calibrated using the JWST pipeline. The analysis was based on a forward-modeling of the images using a multiparameter radiative transfer model coupled to an optical code for coronagraphy processing.Results. The disk is clearly detected at both wavelengths. The slight asymmetry is geometrically consistent with the asymmetry observed in the near-IR, but it is inconsistent the brightness distribution. The observed structure is well reproduced with a model of a disk (or belt) with a critical radius 70 au, a mildly inward-increasing density (index 2) and a steeper decrease outward (index −6). This indication of a filled disk inside the critical radius is inconsistent with sculpting from an inner massive planet. The size distribution of the grains that cause the mid-IR emission is well constrained by the flux ratio at the two wavelengths : 0.45–10 and 0.65–10 μm for silicate and graphite grains, respectively. The minimum size is consistent with predictions of blowout through radiative pressure.Conclusions. We derive a mass of the dust that causes the mid-IR emission of 3.3–5.0 10−3 M⊕. When the larger grains (up to 1 cm) that cause the millimeter emission are included, we extrapolate this mass to 0.10–0.16 M⊕. We point out to that this is fully consistent with ALMA observations of the disk in terms of dust mass and of its millimeter flux. We estimate the average dust temperature in the planetesimal belt to be 74 K, but the temperature range within the whole disk is rather wide: from 40 to 130 K