Precise mass constraints are vital for the characterisation of brown dwarfs and exoplanets. Here we present how the combination of data obtained by Gaia and GRAVITY can help enlarge the sample of substellar companions with measured dynamical masses. We show how the Non-Single-Star (NSS) two-body orbit catalogue contained in Gaia DR3 can be used to inform high-angular-resolution follow-up observations with GRAVITY. Applying the method presented in this work to eight Gaia candidate systems, we detect all eight predicted companions, seven of which were previously unknown and five are of a substellar nature. Among the sample is Gaia DR3 2728129004119806464 B, which - detected at an angular separation of (34.01 ± 0.15) mas from the host - is the closest substellar companion ever imaged. This translates to a semi-major axis of (0.938 ± 0.023) AU. WT 766 B, detected at a greater angular separation, was confirmed to be on an orbit exhibiting an even smaller semi-major axis of (0.676 ± 0.008) AU. The GRAVITY data were then used to break the host-companion mass degeneracy inherent to the Gaia NSS orbit solutions as well as to constrain the orbital solutions of the respective target systems. Knowledge of the companion masses enabled us to further characterise them in terms of their ages, effective temperatures, and radii via the application of evolutionary models. The inferred ages exhibit a distinct bias towards values younger than what is to be expected based on the literature. The results serve as an independent validation of the orbital solutions published in the NSS two-body orbit catalogue and show that the combination of astrometric survey missions and high-angular-resolution direct imaging holds great promise for efficiently increasing the sample of directly imaged companions in the future, especially in the light of Gaia's upcoming DR4 and the advent of GRAVITY+.

Context. High-resolution spectroscopy has the potential to drive a better understanding of the atmospheric composition, physics, and dynamics of young exoplanets and brown dwarfs, bringing clear insights into the formation channel of individual objects. Aims. Using the Keck Planet Imager and Characterizer (KPIC; R « 35 000), we aim to characterize a young brown dwarf HD 984 B. By measuring its C/O and 12 CO/ 13 CO ratios, we expect to gain new knowledge about its origin by confirming the difference in the formation pathways between brown dwarfs and super-Jupiters. Methods. We analysed the KPIC high-resolution spectrum (2.29–2.49 μm) of HD 984 B using an atmospheric retrieval framework based on nested sampling and petitRADTRANS, using both clear and cloudy models. Results. Using our best-fit model, we find C/O = 0.50 ± 0.01 (0.01 is the statistical error) for HD 984 B which agrees with that of its host star within 1 σ (0.40 ± 0.20). We also retrieve an isotopolog 12 CO/ 13 CO ratio of 98 -25 +20 in its atmosphere, which is similar to that of the Sun. In addition, HD 984 B has a substellar metallicity with [Fe/H] =-0.62 -0.02 +0.02 . Finally, we find that most of the retrieved parameters are independent of our choice of retrieval model. Conclusions. From our measured C/O and 12 CO/ 13 CO, the favored formation mechanism of HD 984 B seems to be via gravitational collapse or disk instability and not core accretion, which is a favored formation mechanism for giant exoplanets with m < 13 M Jup and semimajor axis between 10 and 100 au. However, with only a few brown dwarfs with a measured 12 CO/ 13 CO ratio, similar analyses using high-resolution spectroscopy will become essential in order to determine planet formation processes more precisely.

The metal mass fractions of gas giants are a powerful tool to constrain their formation mechanisms and evolution. The metal content is inferred by comparing mass and radius measurements with interior structure and evolution models. In the midst of the JWST, CHEOPS, TESS, and the forthcoming PLATO era, we are at the brink of obtaining unprecedented precision in radius, age and atmospheric metallicity measurements. To prepare for this wealth of data, we present the GAS gianT modeL for Interiors (GASTLI), an easy-to-use, publicly available Python package. The code is optimized to rapidly calculate mass-radius relations, and radius and luminosity thermal evolution curves for a variety of envelope compositions and core mass fractions. Its applicability spans planets with masses $17 \ M_{\oplus} < M < 6 \ M_{Jup}$, and equilibrium temperatures $T_{eq} < 1000$ K. The interior model is stratified in a core composed of water and rock, and an envelope constituted by H/He and metals (water). The interior is coupled to a grid of self-consistent, cloud-free atmospheric models to determine the atmospheric and boundary interior temperature, as well as the contribution of the atmosphere to the total radius. We successfully validate GASTLI by comparing it to previous work and data of the Solar System's gas giants and Neptune. We also test GASTLI on the Neptune-mass exoplanet HAT-P-26 b, finding a bulk metal mass fraction between 0.60-0.78 and a core mass of 8.5-14.4 $M_{\oplus}$. Finally, we explore the impact of different equations of state and assumptions, such as C/O ratio and transit pressure, in the estimation of bulk metal mass fraction. These differences between interior models entail a change in radius of up to 2.5% for Jupiter-mass planets, but more than 10\% for Neptune-mass. These are equivalent to variations in core mass fraction of 0.07, or 0.10 in envelope metal mass fraction.

Context. Since 2019, GRAVITY has provided direct observations of giant planets and brown dwarfs at separations of down to 95 mas from the host star. Some of these observations have provided the first direct confirmation of companions previously detected by indirect techniques (astrometry and radial velocities). Aims. We want to improve the observing strategy and data reduction in order to lower the inner working angle of GRAVITY in dual-field on-axis mode. We also want to determine the current limitations of the instrument when observing faint companions with separations in the 30–150 mas range. Methods. To improve the inner working angle, we propose a fiber off-pointing strategy during the observations to maximize the ratio of companion-light-to-star-light coupling in the science fiber. We also tested a lower-order model for speckles to decouple the companion light from the star light. We then evaluated the detection limits of GRAVITY using planet injection and retrieval in representative archival data. We compare our results to theoretical expectations. Results. We validate our observing and data-reduction strategy with on-sky observations; first in the context of brown dwarf follow-up on the auxiliary telescopes with HD 984 B, and second with the first confirmation of a substellar candidate around the star Gaia DR3 2728129004119806464. With synthetic companion injection, we demonstrate that the instrument can detect companions down to a contrast of 8 × 10 −4 (Δ Κ = 7.7 mag) at a separation of 35 mas, and a contrast of 3 × 10 −5 (Δ Κ = 11 mag) at 100 mas from a bright primary ( K < 6.5), for 30 min exposure time. Conclusions. With its inner working angle and astrometric precision, GRAVITY has a unique reach in direct observation parameter space. This study demonstrates the promising synergies between GRAVITY and Gaia for the confirmation and characterization of substellar companions.

The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs ([U]BV, RIZ, YJH) providing a spectral resolution of similar to 100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 mu m with the goal of extending it to 0.35-2.4 mu m with the addition of an U arm to the BV spectrograph and a separate K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Modularity and fibre-feeding allows ANDES to be placed partly on the ELT Nasmyth platform and partly in the Coude room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature's fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of almost 300 scientists and engineers which include the majority of the scientific and technical expertise in the field that can be found in ESO member states.

Context. Young brown dwarfs exhibit atmospheric characteristics similar to those of super-Jupiters, providing a unique opportunity to study planetary atmospheres. Atmospheric retrievals of high-resolution spectra reveal detailed properties of these objects, with elemental and isotopic ratios offering insights into their formation history. The ESO SupJup Survey, utilising CRIRES+ on the Very Large Telescope, aims to assess the role of C-12/C-13 as a formation tracer. Aims. We present observations of three young brown dwarfs: 2MASS J12003792-7845082, TWA 28, and 2MASS J08561384-1342242. Our goal is to constrain their chemical compositions, thermal profiles, surface gravities, spin rotations, and C-12/C-13. Methods. We conducted atmospheric retrievals of CRIRES+ K-band spectra, coupling the radiative transfer code petitRADTRANS with the Bayesian inference algorithm MultiNest. Results. The retrievals provide a detailed characterisation of the atmospheres of the three objects. We report the volume mixing ratios of the main molecular and atomic species: (H2O)-O-16,(CO)-C-12, HF, Na, Ca, and Ti, including the novel detection of hydrogen fluoride (HF) in the atmosphere of a brown dwarf. We determine C-12/C-13 values of 81(-19)(+28) and 79(-14)(+20) in the atmospheres of TWA 28 and J0856, respectively, with strong significance (>3 sigma). We also report tentative evidence (similar to 2 sigma) of (CO)-C-13 in J1200, at C-12/C-13 = 114(-33)(+69). Additionally, we detect (H2O)-O-18 at moderate significance in J0856 (3.3 sigma) and TWA 28 (2.1 sigma). The retrieved thermal profiles are consistent with hot atmospheres (2300-2600 K) with low surface gravities and slow spins, as expected for young objects. Conclusions. The measured carbon isotope ratios are consistent among the three objects and show no significant deviation from that of the local interstellar medium, suggesting a fragmentation-based formation mechanism similar to star formation. The tentative detection of (H2O)-O-18 in two objects of our sample highlights the potential of high-resolution spectroscopy to probe additional isotope ratios, such as O-16/O-18, in the atmospheres of brown dwarfs and super-Jupiters.

Young, low-mass brown dwarfs orbiting early-type stars, with low mass ratios ( q ≲ 0.01), appear to be intrinsically rare and present a formation dilemma: could a handful of these objects be the highest-mass outcomes of “planetary” formation channels (bottom up within a protoplanetary disk), or are they more representative of the lowest-mass “failed binaries” (formed via disk fragmentation or core fragmentation)? Additionally, their orbits can yield model-independent dynamical masses, and when paired with wide wavelength coverage and accurate system age estimates, can constrain evolutionary models in a regime where the models have a wide dispersion depending on the initial conditions. We present new interferometric observations of the 16 Myr substellar companion HD 136164 Ab (HIP 75056 Ab) made with the Very Large Telescope Interferometer (VLTI)/GRAVITY and an updated orbit fit including proper motion measurements from the Hipparcos–Gaia Catalog of Accelerations. We estimate a dynamical mass of 35 ± 10 M J ( q ∼ 0.02), making HD 136164 Ab the youngest substellar companion with a dynamical mass estimate. The new mass and newly constrained orbital eccentricity ( e = 0.44 ± 0.03) and separation (22.5 ± 1 au) could indicate that the companion formed via the low-mass tail of the initial mass function. Our atmospheric fit to a SPHINX M-dwarf model grid suggests a subsolar C/O ratio of 0.45 and 3 × solar metallicity, which could indicate formation in a circumstellar disk via disk fragmentation. Either way, the revised mass estimate likely excludes bottom-up formation via core accretion in a circumstellar disk. HD 136164 Ab joins a select group of young substellar objects with dynamical mass estimates; epoch astrometry from future Gaia data releases will constrain the dynamical mass of this crucial object further.

ANDES is a high resolution spectrograph for the ELT, with the goal of providing simultaneous spectra with R 100000 from 0.35 to 2.4 micrometer. The baseline of the instrument covers 0.4 - 1.8 micron. Here we present the study on the extension into the K-band (1.95 to 2.45 micron) with its scientific motivation and the technical solution. The spectrograph design is constrained by external limits, but a solution is found that enables key science cases in this wavelength range and closes the gap in ELT high resolution spectroscopy between the ANDES baseline and the METIS instrument. The spectrograph design is throughput-optimized and is fed by the diffraction-limited input from the ANDES SCAO system. We summarize the preliminary optical and cryo-mechanical design. But, as the available mass is one of the critical parameters, we also look into an alternative implementation of the spectrograph with carbon fiber.

Context. Following the recommendations to NASA (in the Astro2020 Decadal survey) and ESA (through the Voyage2050 process), the search for life on exoplanets will be a priority in the next decades. Two concepts for direct imaging space missions are being developed for this purpose: the Habitable Worlds Observatory (HWO) and the Large Interferometer for Exoplanets (LIFE). These two concepts operate in different spectral regimes: HWO is focused on reflected light spectra in the ultraviolet, visible, and near-infrared (UV/VIS/NIR), while LIFE will operate in the mid-infrared (MIR) to capture the thermal emission of temperate exoplanets. Aims. In this study, we aim to assess the potential of HWO and LIFE to characterize a cloud-free Earth twin orbiting a Sun-like star at a distance of 10 pc, both as separate missions and in synergy with each other. We aim to quantify the increase in information that can be gathered by joint atmospheric retrievals on a habitable planet. Methods. We performed Bayesian retrievals on simulated data obtained by an HWO-like mission and a LIFE-like one separately, then jointly. We considered the baseline spectral resolutions currently assumed for these concepts and used two increasingly complex noise simulations, obtained using state-of-the-art noise simulators. Results. An HWO-like concept would allow one to strongly constrain H2O, O-2, and O-3 in the atmosphere of a cloud-free Earth twin, while the atmospheric temperature profile is not well constrained (with an average uncertainty approximate to 100 K). LIFE-like observations would strongly constrain CO2, H2O, and O-3 and provide stronger constraints on the thermal atmospheric structure and surface temperature (down to approximate to 10 K uncertainty). For all the investigated scenarios, both missions would provide an upper limit on CH4. A joint retrieval on HWO and LIFE data would accurately define the atmospheric thermal profile and planetary parameters. It would decisively constrain CO2, H2O, O-2, and O-3 and find weak constraints on CO and CH4. The significance of the detection is in all cases greater than or equal to the single-instrument retrievals. Conclusions. Both missions provide specific information that is relevant for the characterization of a terrestrial habitable exoplanet, but the scientific yield can be maximized by considering synergistic studies of UV/VIS/NIR+MIR observations. The use of HWO and LIFE together will provide stronger constraints on biosignatures and life indicators, with the potential to be transformative for the search for life in the Universe.

Context. A low-mass companion potentially in the brown dwarf mass regime was discovered on a similar to 12 yr orbit (similar to 5.5 au) around HD 167665 using radial velocity (RV) monitoring. Joint RV-astrometry analyses confirmed that HD 167665B is a brown dwarf with precisions on the measured mass of similar to 4-9%. Brown dwarf companions with measured mass and luminosity are valuable for testing formation and evolutionary models. However, its atmospheric properties and luminosity are still unconstrained, preventing detailed tests of evolutionary models. Aims. We further characterize the HD 167665 system by measuring the luminosity and refining the mass of its companion and reassessing the stellar age. Methods. We present new high-contrast imaging data of the star and of its close-in environment from SPHERE and GRAVITY, which we combined with RV data from CORALIE and HIRES and astrometry from HIPPARCOS and Gaia. Results. The analysis of the host star properties indicates an age of 6.20 +/- 1.13 Gyr. GRAVITY reveals a point source near the position predicted from a joint fit of RV data and HIPPARCOS-Gaia proper motion anomalies. Subsequent SPHERE imaging confirms the detection and reveals a faint point source of contrast of Delta H2 = 10.95 +/- 0.33 mag at a projected angular separation of similar to 180 mas. A joint fit of the high-contrast imaging, RV, and HIPPARCOS intermediate astrometric data together with the Gaia astrometric parameters constrains the mass of HD 167665B to similar to 1.2%, 60.3 +/- 0.7 M-J. The SPHERE colors and spectrum point to an early or mid-T brown dwarf of spectral type T4(-2)(+1). Fitting the SPHERE spectrophotometry and GRAVITY spectrum with synthetic spectra suggests an effective temperature of similar to 1000-1150 K, a surface gravity of similar to 5.0-5.4 dex, and a bolometric luminosity log(L/L-circle dot)=-4.892(-0.028)(+0.024) dex. The mass, luminosity, and age of the companion can only be reproduced within 3 sigma by the hybrid cloudy evolutionary models of Saumon & Marley (2008, ApJ, 689, 1327), whereas cloudless evolutionary models underpredict its luminosity.

Context. HD 209458 b is one of the most studied exoplanets to date. Despite this, atmospheric characterisation studies yielded inconsistent species detections and abundances. Values reported for the C/O ratio range from approximate to 0.1 to 1.0. Of particular interest is the simultaneous detection of H2O and HCN reported by some studies using high-resolution ground-based observations, which would require the atmospheric C/O ratio to be fine-tuned to a narrow interval around 1. HCN has however not been detected from recent space-based observations. Aims. We aim to provide an independent study of HD 209458 b's atmosphere with high-resolution observations, in order to infer the presence of several species, including H2O and HCN. Methods. We observed four primary transits of HD 209458 b at a high resolution (R approximate to 92000) with CRIRES+ in the near infrared (band H, 1.431243-1.837253 mu m). After reducing the data with pycrires, we prepared the data using the SysRem algorithm and performed a cross-correlation (CCF) analysis of the transmission spectra. We also compared the results with those obtained from simulated datasets constructed by combining the Exo-REM self-consistent model with the petitRADTRANS package. Results. Combining the four transits, we detect H2O with a signal-to-noise CCF metric of 8.7 sigma. This corresponds to a signal emitted at Kp = 151.3-23.4+31.1 km s(-1) and blueshifted by -6-2+1 km s(-1), consistent with what is expected for HD 209458 b. We do not detect any other species among C2H2, CH4, CO, CO2, H2S, HCN, and NH3. Comparing this with our simulated datasets, this result is consistent with a C/O ratio of 0.1 and an opaque cloud top pressure of 50 Pa, at a 3 times solar metallicity. This would also be consistent with recent JWST observations. However, none of the simulated results obtained with a bulk C/O ratio of 0.8, a value suggested by previous studies using GIANO-B and CRIRES, are consistent with our observations.

Context . It has been proposed that the distinct formation and evolutionary pathways of exoplanets and brown dwarfs may affect the chemical and isotopic content of their atmospheres. Recent work has indeed shown differences in the 12 C/ 13 C isotope ratio, which have provisionally been attributed to the top-down formation of brown dwarfs and the core accretion pathway of super-Jupiters. Aims . The ESO SupJup Survey is aimed at disentangling the formation pathways of isolated brown dwarfs and planetary-mass companions using chemical and isotopic tracers. The survey utilises high-resolution spectroscopy with the recently upgraded CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES + ) at the Very Large Telescope, covering a total of 49 targets. Here, we present the first results of this survey: an atmospheric characterisation of DENIS J0255-4700, an isolated brown dwarf near the L-T transition. Methods . We analysed its observed CRIRES + K -band spectrum using an atmospheric retrieval framework in which the radiative transfer code petitRADTRANS was coupled with the PyMultiNest sampling algorithm. Gaussian processes were employed to model inter-pixel correlations. In addition, we adopted an updated parameterisation of the pressure-temperature profile. Results . Abundances of CO, H 2 O, CH 4 , and NH 3 were retrieved for this fast-rotating L-dwarf. The ExoMol H 2 O line list provides a significantly better fit than that of HITEMP. A free-chemistry retrieval is strongly favoured over equilibrium chemistry, caused by an under-abundance of CH 4 . The free-chemistry retrieval constrains a super-solar C/O-ratio of ~0.68 and a solar metallicity. We find tentative evidence (~3 σ ) for the presence of 13 CO, with a constraint on the isotopologue ratio of 12 CO/ 13 CO = 184 −40 +61 and a lower limit of ≳97, which suggests a depletion of 13 C compared to the local interstellar medium ( 12 C/ 13 C ~ 68). Conclusions . High-resolution, high signal-to-noise K -band spectra provide an excellent means of constraining the chemistry and isotopic content of sub-stellar objects, which is the main objective of the ESO SupJup Survey.

With four companions at separations from 16 to 71 au, HR 8799 is a unique target for direct imaging, presenting an opportunity for the comparative study of exoplanets with a shared formation history. Combining new VLTI/GRAVITY observations obtained within the ExoGRAVITY program with archival data, we perform a systematic atmospheric characterisation of all four planets. We explore different levels of model flexibility to understand the temperature structure, chemistry and clouds of each planet using both petitRADTRANS atmospheric retrievals and fits to self-consistent radiative-convective equilibrium models. Using Bayesian Model Averaging to combine multiple retrievals, we find that the HR 8799 planets are highly enriched in metals, with [M/H] $\gtrsim$1, and have stellar to super-stellar C/O ratios. The C/O ratio increases with increasing separation from $0.55^{+0.12}_{-0.10}$ for d to $0.78^{+0.03}_{-0.04}$ for b, with the exception of the innermost planet which has a C/O ratio of $0.87\pm0.03$. By retrieving a quench pressure and using a disequilibrium chemistry model we derive vertical mixing strengths compatible with predictions for high-metallicity, self-luminous atmospheres. Bayesian evidence comparisons strongly favour the presence of HCN in HR 8799 c and e, as well as CH$_{4}$ in HR 8799 c, with detections at $>5\sigma$ confidence. All of the planets are cloudy, with no evidence for patchiness. The clouds of c, d and e are best fit by silicate clouds lying above a deep iron cloud layer, while the clouds of the cooler HR 8799 b are more likely composed of Na$_{2}$S. With well defined atmospheric properties, future exploration of this system is well positioned to unveil further detail in these planets, extending our understanding of the composition, structure, and formation history of these siblings.

Context. High-resolution spectrographs fed by adaptive optics (AO) provide a unique opportunity to characterize directly imaged exoplanets. Observations with such instruments allow us to probe the atmospheric composition, spin rotation, and radial velocity of the planet, thereby helping to reveal information on its formation and migration history. The recent upgrade of the Cryogenic High-Resolution Infrared Echelle Spectrograph (CRIRES+) at the VLT makes it a highly suitable instrument for characterizing directly imaged exoplanets. Aims. In this work, we report on observations of beta Pictoris b with CRIRES+ and use them to constrain the planets atmospheric properties and update the estimation of its spin rotation. Methods. The data were reduced using the open-source pycrires package. We subsequently forward-modeled the stellar, planetary, and systematic contribution to the data to detect molecules in the planet's atmosphere. We also used atmospheric retrievals to provide new constraints on its atmosphere. Results. We confidently detected water and carbon monoxide in the atmosphere of beta Pictoris b and retrieved a slightly sub-solar carbon-to-oxygen ratio, which is in agreement with previous results. The interpretation is hampered by our limited knowledge of the C/O ratio of the host star. We also obtained a much improved constraint on its spin rotation of 19.9 +/- 1.0 kms(-1), which gives a rotation period of 8.7 +/- 0.8 h, assuming no obliquity. We find that there is a degeneracy between the metallicity and clouds, but this has minimal impact on the retrieved C/O, upsilon sin i, and radial velocity. Our results show that CRIRES+ is performing well and stands as a highly useful instrument for characterizing directly imaged planets.

We present simultaneous 0.65-2.5 microns medium resolution (3300 < R < 8100) VLT/X-Shooter spectra of the young low-mass (19+/-5MJup) L-T transition object VHS 1256-1257 b, a known spectroscopic analogue of HR8799d. The companion is a prime target for the JWST Early Release Science (ERS) and one of the highest-amplitude variable brown-dwarf known to date. We compare the spectrum to the custom grids of cloudless ATMO models exploring different atmospheric composition with the Bayesian inference tool ForMoSA. We also re-analyze low-resolution HST/WFC3 1.10-1.67 microns spectra at minimum and maximum variability to contextualize the X-Shooter data interpretation. The models reproduce the slope and most molecular absorption from 1.10 to 2.48 microns self-consistently but fail to provide a radius consistent with evolutionary model predictions. They do not reproduce consistently the optical spectrum and the depth of the K I doublets in the J-band. We derive Teff = 1380+/-54 K, log(g) = 3.97+/-0.48 dex, [M/H] = 0.21+/-0.29, and C/O > 0.63. Our inversion of the HST/WFC3 spectra suggests a relative change of 27+6-5 K of the disk-integrated Teff correlated with the near-infrared brightness. Our data anchor the characterization of that object in the near-infrared and could be used jointly to the ERS mid-infrared data to provide the most detailed characterization of an ultracool dwarf to date.

Long term precise radial velocity (RV) monitoring of the nearby star HD206893, as well as anomalies in the system proper motion, have suggested the presence of an additional, inner companion in the system. Here we describe the results of a multi-epoch search for the companion responsible for this RV drift and proper motion anomaly using the VLTI/GRAVITY instrument. Utilizing information from ongoing precision RV measurements with the HARPS spectrograph, as well as Gaia host star astrometry, we report a high significance detection of the companion HD206893c over three epochs, with clear evidence for Keplerian orbital motion. Our astrometry with $\sim$50-100 $\mu$arcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7$^{+1.2}_{-1.0}$ M$_{\rm Jup}$ and an orbital separation of 3.53$^{+0.08}_{-0.06}$ au for HD206893c. Our fits to the orbits of both companions in the system utilize both Gaia astrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore derive an age of $155\pm15$ Myr. We find that theoretical atmospheric/evolutionary models incorporating deuterium burning for HD206893c, parameterized by cloudy atmospheres provide a good simultaneous fit to the luminosity of both HD206893B and c. In addition to utilizing long-term RV information, this effort is an early example of a direct imaging discovery of a bona fide exoplanet that was guided in part with Gaia astrometry. Utilizing Gaia astrometry is expected to be one of the primary techniques going forward to identify and characterize additional directly imaged planets. Lastly, this discovery is another example of the power of optical interferometry to directly detect and characterize extrasolar planets where they form at ice-line orbital separations of 2-4\,au.

Tension remains between the observed and modeled properties of substellar objects, but objects in binary orbits, with known dynamical masses, can provide a way forward. HD 72946 B is a recently imaged brown dwarf companion to a nearby, solar-type star. We achieve ∼100 μ as relative astrometry of HD 72946 B in the K band using VLTI/GRAVITY, unprecedented for a benchmark brown dwarf. We fit an ensemble of measurements of the orbit using orbitize! and derive a strong dynamical mass constraint M B = 69.5 ± 0.5 M Jup assuming a strong prior on the host star mass M A = 0.97 ± 0.01 M ⊙ from an updated stellar analysis. We fit the spectrum of the companion to a grid of self-consistent BT-Settl-CIFIST model atmospheres, and perform atmospheric retrievals using petitRADTRANS . A dynamical mass prior only marginally influences the sampled distribution of effective temperature, but has a large influence on the surface gravity and radius, as expected. The dynamical mass alone does not strongly influence retrieved pressure–temperature or cloud parameters within our current retrieval setup. Independently of the cloud prescription and prior assumptions, we find agreement within ±2 σ between the C/O of the host (0.52 ± 0.05) and brown dwarf (0.43–0.63), as expected from a molecular cloud collapse formation scenario, but our retrieved metallicities are implausibly high (0.6–0.8) in light of the excellent agreement of the data with the solar-abundance model grid. Future work on our retrieval framework will seek to resolve this tension. Additional study of low surface gravity objects is necessary to assess the influence of a dynamical mass prior on atmospheric analysis.

Giant exoplanets have been directly imaged over orders of magnitude of orbital separations, prompting theoretical and observational investigations of their formation pathways. In this paper, we present new VLTI/GRAVITY astrometric data of HIP 65426 b, a cold, giant exoplanet which is a particular challenge for most formation theories at a projected separation of 92 au from its primary. Leveraging GRAVITY's astrometric precision, we present an updated eccentricity posterior that disfavors large eccentricities. The eccentricity posterior is still prior dependent, and we extensively interpret and discuss the limits of the posterior constraints presented here. We also perform updated spectral comparisons with self-consistent forward-modeled spectra, finding a best-fit ExoREM model with solar metallicity and C/O = 0.6. An important caveat is that it is difficult to estimate robust errors on these values, which are subject to interpolation errors as well as potentially missing model physics. Taken together, the orbital and atmospheric constraints paint a preliminary picture of formation inconsistent with scattering after disk dispersal. Further work is needed to validate this interpretation. Analysis code used to perform this work is available on GitHub: https://github.com/sblunt/hip65426.

[Full abstract in the paper] We aim to better constrain the atmospheric properties of the directly imaged exoplanet 51~Eri~b by using a retrieval approach on higher signal-to-noise data than previously reported. In this context, we also compare the results of using the atmospheric retrieval code \texttt{petitRADTRANS} vs a self-consistent model to fit atmospheric parameters. We present a higher signal-to-noise $YH$ spectrum of the planet and revised $K1K2$ photometry (M$_{K1} = 15.11 \pm 0.04$ mag, M$_{K2} = 17.11 \pm 0.38$ mag). The best-fit parameters obtained using an atmospheric retrieval differ from previous results using self-consistent models. In general, we find that our solutions tend towards cloud-free atmospheres (e.g. log $\tau_{\rm clouds} = -5.20 \pm 1.44$). For our ``nominal'' model with new data, we find a lower metallicity ([Fe/H] $= 0.26\pm$0.30 dex) and C/O ratio ($0.38\pm0.09$), and a slightly higher effective temperature (T$_{\rm{eff}} = 807\pm$45 K) than previous studies. The surface gravity (log $g = 4.05\pm0.37$) is in agreement with the reported values in the literature within uncertainties. We estimate the mass of the planet to be between 2 and 4 M$_{\rm{Jup}}$. When comparing with self-consistent models, we encounter a known correlation between the presence of clouds and the shape of the $P-T$ profiles. Our findings support the idea that results from atmospheric retrievals should not be discussed in isolation, but rather along with self-consistent temperature structures obtained using the retrieval's best-fit parameters.

Aims.HD 206893 is a nearby debris disk star that hosts a previously identified brown dwarf companion with an orbital separation of ∼10 au. Long-term precise radial velocity (RV) monitoring, as well as anomalies in the system proper motion, has suggested the presence of an additional, inner companion in the system.Methods.Using information from ongoing precision RV measurements with the HARPS spectrograph, as well asGaiahost star astrometry, we have undertaken a multi-epoch search for the purported additional planet using the VLTI/GRAVITY instrument.Results.We report a high-significance detection over three epochs of the companion HD 206893c, which shows clear evidence for Keplerian orbital motion. Our astrometry with ∼50−100 μarcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7$ ^{+1.2}_{-1.0} $MJupand an orbital separation of 3.53$ ^{+0.08}_{-0.06} $ au for HD 206893c. Our fits to the orbits of both companions in the system use bothGaiaastrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore allow us to derive an age of 155 ± 15 Myr for the system. We find that theoretical atmospheric and evolutionary models that incorporate deuterium burning for HD 206893c, parameterized by cloudy atmosphere models as well as a “hybrid sequence” (encompassing a transition from cloudy to cloud-free), provide a good simultaneous fit to the luminosity of both HD 206893B and c. Thus, accounting for both deuterium burning and clouds is crucial to understanding the luminosity evolution of HD 206893c.Conclusions.In addition to using long-term RV information, this effort is an early example of a direct imaging discovery of a bona fide exoplanet that was guided in part byGaiaastrometry. UtilizingGaiaastrometry is expected to be one of the primary techniques going forward for identifying and characterizing additional directly imaged planets. In addition, HD 206893c is an example of an object narrowly straddling the deuterium-burning limit but unambiguously undergoing deuterium burning. Additional discoveries like this may therefore help clarify the discrimination between a brown dwarf and an extrasolar planet. Lastly, this discovery is another example of the power of optical interferometry to directly detect and characterize extrasolar planets where they form, at ice-line orbital separations of 2−4 au.