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The mid-infrared spectrum of β Pictoris b
No full textInternational audienceFew spectra of directly imaged exoplanets have been obtained in the mid-infrared (>3 μm). This region is particularly rich in molecular spectral signatures, whose measurements can help recover atmospheric parameters and provide a better understanding of giant planet formation and atmospheric dynamics. In recent years, exoplanet interferometry with the VLTI/GRAVITY instrument has provided medium-resolution spectra of a dozen sub-stellar companions in the near-infrared. The 100 meter interferometric baselines enable the stellar and planetary signals to be efficiently disentangled at close angular separations (<0.3″). We aim to extend this technique to the mid-infrared using MATISSE, the VLTI’s mid-infrared spectro-interferometer. We take advantage of the fringe tracking and off-axis pointing capabilities recently brought by the GRA4MAT upgrade. Using this new mode, we observed the giant planet β Pictoris b in L and M bands (2.75–5 μm) at a spectral resolution of 500. We developed a method to correct chromatic dispersion and non-common path effects in the fringe phase and modelled the planet astrometry and stellar contamination. We obtained a high-signal-to-noise spectrum of β Pictoris b, showing the planet continuum in the L (for the first time) and M bands, which contains broad absorption features of H 2 O and CO. In conjunction with a new GRAVITY spectrum, we modelled it with the ForMoSA nested sampling tool and the Exo-REM grid of atmospheric models, and found a solar carbon-to-oxygen ratio in the planet atmosphere. This study opens the way to the characterization of fainter and closer-in planets with MATISSE, which could complement the JWST at angular separations too close for it to obtain exoplanet spectra. Starting in 2025, the new adaptive optics system brought by the GRAVITY+ upgrade will further extend the detection limits of MATISSE
Edge-On Disk Study (EODS) III: Molecular Stratification in the Flying Saucer Disk
No full textInternational audienceInvestigating the vertical distribution of molecular content in protoplanetary disks remains difficult in most disks mildly inclined along the line of sight. In contrast, edge-on disks provide a direct (tomographic) view of the 2D molecular brightness. Aims . We study the radial and vertical molecular distribution as well as the gas temperature and density by observing the Keplerian edge-on disk surrounding the Flying Saucer, a Class II object located in Ophiuchus. Methods . We used new and archival ALMA data to perform a tomography of 12 CO, 13 CO, C 18 O, CN, HCN, CS, H 2 CO, c-C 3 H 2 , N 2 D + , DCN, and 13 CS. We analyzed molecular tomographies and modeled data using the radiative transfer code D ISK F IT . Results . We directly measured the altitude above the mid-plane for each observed species. For the first time, we unambiguously demonstrate the presence of a common molecular layer and measure its thickness. Most molecules are located at the same altitude versus radius. Beyond CO, as predicted by chemical models, the CN emission traces the upper boundary of the molecular layer, whereas the deuterated species (DCN and N 2 D + ) reside below one scale height. Our best fits from D ISK F IT show that most observed transitions in the molecular layer are thermalized because their excitation temperature is the same, around ~17-20K. Conclusions . These long-integration observations clearly reveal a molecular layer predominantly located around one to two scale heights at a temperature above the CO freeze-out temperature. The deuterated molecules are closer to the mid-plane, and N 2 D + may be a good proxy for the CO snowline. Some molecules, such as CN and H 2 CO, are likely influenced by the disk environment, at least beyond the millimeter dust disk radius. The direct observation of the molecular stratification opens the door to detailed chemical modeling in a disk that appears representative of T Tauri disks
Euclid preparation LXXIII. Spatially resolved stellar populations of local galaxies with Euclid: A proof of concept using synthetic images with the TNG50 simulation
No full textInternational audienceThe European Space Agency's Euclid mission will observe approximately 14,000 of the extragalactic sky and deliver high-quality imaging for many galaxies. The depth and high spatial resolution of the data will enable a detailed analysis of stellar population properties of local galaxies. In this study, we test our pipeline for spatially resolved SED fitting using synthetic images of Euclid, LSST, and GALEX generated from the TNG50 simulation. We apply our pipeline to 25 local simulated galaxies to recover their resolved stellar population properties. We produce 3 types of data cubes: GALEX + LSST + Euclid, LSST + Euclid, and Euclid-only. We perform the SED fitting tests with two SPS models in a Bayesian framework. Because the age, metallicity, and dust attenuation estimates are biased when applying only classical formulations of flat priors, we examine the effects of additional priors in the forms of mass-age- relations, constructed using a combination of empirical and simulated data. Stellar-mass surface densities can be recovered well using any of the 3 data cubes, regardless of the SPS model and prior variations. The new priors then significantly improve the measurements of mass-weighted age and compared to results obtained without priors, but they may play an excessive role compared to the data in determining the outcome when no UV data is available. The spatially resolved SED fitting method is powerful for mapping the stellar populations of galaxies with the current abundance of high-quality imaging data. Our study re-emphasizes the gain added by including multiwavelength data from ancillary surveys and the roles of priors in Bayesian SED fitting. With the Euclid data alone, we will be able to generate complete and deep stellar mass maps of galaxies in the local Universe, thus exploiting the telescope's wide field, NIR sensitivity, and high spatial resolution
Broadband mid-infrared spectroscopy in a CH4 + O2 plasma glow discharge
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A Preliminary Search for Planets and Exozodiacal Emission Around α Centauri A with JWST/MIRI
No full textInternational audienceAbstract We present F1550C (15.5 μ m) coronagraphic imaging observations of the nearest solar-type star α Cen A using the James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI). The observations, executed in 2025 February, were compromised by having only one successful roll and degraded performance due to a position mismatch (Δ r ∼ 10 mas) between α Cen A and the best-matching reference observation behind the MIRI coronagraph. We set preliminary upper limits on both the presence of a planet and an exozodiacal dust disk. The observations are sensitive to a planet heated by α Cen A (200–250 K) with a radius ≳1 R Jup at a separation of 1 . ″ 5 (2 au) and zodiacal dust emission at the level of ≳5–10 times the brightness of our own zodiacal cloud. A complete analysis of all JWST/MIRI observations of α Cen A is forthcoming in Paper I (Beichman & Sanghi et al. 2025, in preparation) and Paper II (Sanghi & Beichman et al. 2025, in preparation)