JWST-TST High Contrast: First Direct Spectroscopy of GJ 504 b reveals Clouds and Possible Metal Enrichment
2026/06/17 by Aneesh Baburaj, Jean-Baptiste Ruffio, Marshall Perrin +27 · 1 voice
Physics and Astronomy · #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.3847/1538-3881/ae6919
Abstract
Characterizing the coldest directly imaged companions through direct spectroscopy has only recently become possible with the James Webb Space Telescope. We present moderate-resolution (R ∼ 2,700) spectroscopic observations of the directly imaged planetary-mass companion (PMC), GJ 504 b, using the JWST/NIRSpec. As the coldest imaged PMC of the pre-JWST era GJ 504 b is too faint for ground-based spectroscopy, with only photometric observations possible. Leveraging advanced post-processing techniques with a forward modeling framework, we detect the companion at high signal-to-noise (S/N>300). We also present the first successful PSF subtraction with angular differential imaging (ADI) in the NIRSpec point cloud, detecting GJ 504 b at S/N>10 and reaching contrast limits <10-4. The extracted 2.9--5.3 μm spectra show strong signatures of several molecular species, including H2O, 12C16O, CH4, CO2, NH3, H2S, 13C16O, and 12C18O. Atmospheric modeling of the spectra using petitRADTRANS, yields an effective temperature = 564±4 K, surface gravity logg = 4.87+0.13-0.12, metallicity [M/H] = 0.67+0.13-0.12, C/O ratio = 0.64+0.02-0.02, interstellar 12C/13C and 16O/18O isotopologue ratios, and strong evidence of disequilibrium chemistry and salt clouds. The retrieved parameters indicate a mass 25.2+8.4-6.0 MJup, which is in agreement with the mass range (19--27 MJup) obtained from ATMO evolutionary models, implying an age of 2.5--4.0 Gyr. Lastly, we compare the abundances of GJ 504 b to its primary, obtaining a stellar abundance of sulfur (S), super-stellar carbon (C), and possibly, oxygen (O). The observed metal enrichment tentatively supports planet-like formation, but does not entirely exclude stellar abundances for GJ 504 b.
Citations
- Eating planets makes you younger: The magnetic dynamo rejuvenation of GJ 504 by planetary engulfment
- The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas
- Jupiter-like uniform metal enrichment in a system of multiple giant exoplanets
- The Diversity of Cold Worlds: Age and Characterization of the Exoplanet COCONUTS-2b
- Chemical and Isotopic Homogeneity Between the L Dwarf CD-35 2722 B and its Early M Host Star
- A High-Resolution Spectroscopic Survey of Directly Imaged Companion Hosts: II. Diversity in C/O Ratios among Host Stars
- JWST-TST High Contrast: Medium-resolution spectroscopy reveals a carbon-rich circumplanetary disk around the young accreting exoplanet Delorme 1 AB b
- Ross 458c: Gas Giant or Brown Dwarf?
- Revising the Giant Planet Mass–Metallicity Relation: Deciphering the Formation Sequence of Giant Planets
- Evidence for SiO cloud nucleation in the rogue planet PSO J318
- JWST Coronagraphic Images of 14 Her c: a Cold Giant Planet in a Dynamically Hot, Multi-planet System
- The Sonora Substellar Atmosphere Models. V. A Correction to the Disequilibrium Abundance of CO2 for Sonora Elf Owl
- Evidence for a sub-jovian planet in the young TWA7 disk
- First unambiguous detection of ammonia in the atmosphere of a planetary mass companion with JWST/MIRI coronagraphs
- VLTI/GRAVITY Observations of AF Lep b: Preference for Circular Orbits, Cloudy Atmospheres, and a Moderately Enhanced Metallicity
- easyCHEM: A Python package for calculating chemical equilibrium abundances in exoplanet atmospheres
- Disequilibrium Chemistry, Diabatic Thermal Structure, and Clouds in the Atmosphere of COCONUTS-2b
- A High-Resolution Spectroscopic Survey of Directly Imaged Companion Hosts: I. Determination of diagnostic stellar abundances for planet formation and composition
- JWST-TST High Contrast: Spectroscopic Characterization of the Benchmark Brown Dwarf HD 19467 B with the NIRSpec Integral Field Spectrograph
- A temperate super-Jupiter imaged with JWST in the mid-infrared
- A Tale of Two Molecules: The Underprediction of CO2 and Overprediction of PH3 in Late T and Y Dwarf Atmospheric Models
- A Tale of Two Molecules: The Underprediction of CO2 and Overprediction of PH3 in Late T and Y Dwarf Atmospheric Models
- Are these planets or brown dwarfs? Broadly solar compositions from high-resolution atmospheric retrievals of ~10-30 M_\textrmJup companions
- Four-of-a-kind? Comprehensive atmospheric characterisation of the HR 8799 planets with VLTI/GRAVITY
- High-precision atmospheric characterization of a Y dwarf with JWST NIRSpec G395H spectroscopy: isotopologue, C/O ratio, metallicity, and the abundances of six molecular species
- JWST-TST High Contrast: Asymmetries, dust populations and hints of a collision in the β Pictoris disk with NIRCam and MIRI
- Validation of elemental and isotopic abundances in late-M spectral types with the benchmark HIP 55507 AB system
- JWST measurements of 13C, 18O and 17O in the atmosphere of super-Jupiter VHS 1256 b
- Early Accretion of Large Amounts of Solids for Directly-Imaged Exoplanets
- ELemental abundances of Planets and brown dwarfs Imaged around Stars (ELPIS): I. Potential Metal Enrichment of the Exoplanet AF Lep b and a Novel Retrieval Approach for Cloudy Self-luminous Atmospheres
- Assessing the C/O Ratio Formation Diagnostic: A Potential Trend with Companion Mass
- The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package*
- The Near-Infrared Spectrograph (NIRSpec) on theJames WebbSpace Telescope
- Array Programming with NumPy
- SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
- petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
- Exoplanetary Atmospheres: Key Insights, Challenges and Prospects
- dynesty: A Dynamic Nested Sampling Package for Estimating Bayesian Posteriors and Evidences
- astroquery: An Astronomical Web-Querying Package in Python
- The GJ 504 system revisited. Combining interferometric, radial velocity, and high contrast imaging data
- Lithium abundance patterns of late-F stars: an in-depth analysis of the lithium desert
- The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
- A self-consistent cloud model for brown dwarfs and young giant exoplanets: comparison with photometric and spectroscopic observations
- Improving and Assessing Planet Sensitivity of the GPI Exoplanet Survey with a Forward Model Matched Filter
- The Y-Type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry and Near-Infrared Spectroscopy
- Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
- Abundances in the Local Region II: F, G and K Dwarfs and Subgiants
- The Role of Ice Compositions for Snowlines and the C/N/O Ratios in Active Disks
- Forward and Inverse Modeling of the Emission and Transmission Spectrum of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds
- A critical reassessment of the fundamental properties of GJ 504: Chemical composition and age
- The radial dependence of pebble accretion rates: A source of diversity in planetary systems
- Gravitational Instabilities in Circumstellar Disks
- Interpreting the photometry and spectroscopy of directly imaged planets: a new atmospheric model applied to beta Pictoris b and SPHERE observations
- ExoMol line lists – VII. The rotation–vibration spectrum of phosphine up to 1500 K
- Transmission spectral properties of clouds for hot Jupiter exoplanets
- The ancient heritage of water ice in the solar system
- Towards Precise Ages and Masses of Free Floating Planetary Mass Brown Dwarfs
- Astropy: A Community Python Package for Astronomy
- Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
- The D/H ratio in the atmospheres of Uranus and Neptune from Herschel PACS observations
- Accurate and homogeneous abundance patterns in solar-type stars of the solar neighbourhood: a chemo-chronological analysis
- Metallicity of solar-type stars with debris discs and planets
- HITEMP, the high-temperature molecular spectroscopic database
- Parent Stars of Extrasolar Planets. X. Lithium Abundances and vsini Revisited
- The Evolution of L and T Dwarfs in Color‐Magnitude Diagrams
- Physical and Spectral Characteristics of the T8 and Later-Type Dwarfs
- Binaries and the L Dwarf/T Dwarf Transition
- Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition
- SDSS J1534+1615AB: A Novel T Dwarf Binary Found with Keck Laser Guide Star Adaptive Optics and the Potential Role of Binarity in the L/T Transition
- Improved HCN/HNC linelist, model atmospheres and synthetic spectra for WZ Cas
- Angular Differential Imaging: A Powerful High‐Contrast Imaging Technique
- On the correlation of elemental abundances with kinematics among galactic disk stars
- Identifying Young Brown Dwarfs Using Gravity-Sensitive Spectral Features
- SINFONI - Integral Field Spectroscopy at 50 milli-arcsecond resolution with the ESO VLT
- Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458
- Precipitating Condensation Clouds in Substellar Atmospheres
- Spectral Energy Distributions of T Tauri Stars With Passive Circumstellar Disks
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