VLTI/GRAVITY Observations and Characterization of the Brown Dwarf Companion HD 72946 B

Abstract

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 the nearby, solar type star. We achieve $\sim 100\mu \mathrm{as}$ 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 ${\mathrm{M}}_{\mathrm{B}}=69.5\pm 0.5{\mathrm{M}}_{\mathrm{Jup}}$ assuming a strong prior on the host star mass ${\mathrm{M}}_{\mathrm{A}}=0.97\pm 0.01{\mathrm{M}}_{\odot }$ 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 on 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. Independent of cloud prescription and prior assumptions, we find agreement within $\pm 2\sigma$ between the C/O ratio of the host ($0.52\pm 0.05)$ and brown dwarf ($0.43$ to $0.63$), as expected from a molecular cloud collapse formation scenario, but our retrieved metallicities are implausibly high ($0.6-0.8$) in light of an 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.

Accepted for publication in the Astrophysical Journal. 32 pages, 14 figures, 7 tables. v2&3 correct errors in co-author's affiliations, figure rendering, and some grant acknowledgements

References in corpus (54)

• The Gaia mission
• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• The chemical make-up of the Sun: A 2020 vision
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• The 0.8-14.5 micron Spectra of Mid-L to Mid-T Dwarfs: Diagnostics of Effective Temperature, Grain Sedimentation, Gas Transport, and Surface Gravity
• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation
• The Hipparcos-Gaia Catalog of Accelerations: Gaia EDR3 Edition
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• Observational constraints on the origin of the elements. IV: The standard composition of the Sun
• New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars
• Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
• Brown dwarf formation by gravitational fragmentation of massive, extended protostellar discs
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• Gaia Data Release 3: Apsis II -- Stellar Parameters
• orbitize!: A Comprehensive Orbit-fitting Software Package for the High-contrast Imaging Community
• Abundances in the Local Region II: F, G and K Dwarfs and Subgiants
• Peering into the formation history of beta Pictoris b with VLTI/GRAVITY long baseline interferometry
• Constraining the Nature of the PDS 70 Protoplanets with VLTI/GRAVITY
• The GALAH Survey: Non-LTE departure coefficients for large spectroscopic surveys
• Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158
• C/O Ratios of Stars with Transiting Hot Jupiter Exoplanets
• linemake: An Atomic and Molecular Line List Generator
• Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope
• The mass of Beta Pictoris c from Beta Pictoris b orbital motion
• Keck/NIRC2 $L$'-Band Imaging of Jovian-Mass Accreting Protoplanets around PDS 70
• Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. II. Emergence and Sedimentation of Silicate Clouds in L Dwarfs, and Analysis of the Full M5--T9 Field Dwarf Spectroscopic Sample
• Improved Dynamical Masses for Six Brown Dwarf Companions Using Hipparcos and Gaia EDR3
• A Clear View of a Cloudy Brown Dwarf Companion from High-Resolution Spectroscopy
• Thermo-compositional diabatic convection in the atmospheres of brown dwarfs and in Earth's atmosphere and oceans
• Probing the Extent of Vertical Mixing in Brown Dwarf Atmospheres with Disequilibrium Chemistry
• The effect of stellar activity on the spectroscopic stellar parameters of the young solar twin HIP 36515
• Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs
• Evidence that the Hot Jupiter WASP-77 A b Formed Beyond Its Parent Protoplanetary Disk's H2O Ice Line
• Retrieving the C and O Abundances of HR 7672~AB: a Solar-Type Primary Star with a Benchmark Brown Dwarf
• HIP 114328: a new refractory-poor and Li-poor solar twin
• Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-Dwarf Companion in the Hyades
• Retrieval Study of Brown Dwarfs Across the L-T Sequence
• Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph -- III. Dust Grains in Young L Dwarf Atmospheres Are Heavier
• Revisiting the atmosphere of the exoplanet 51 Eridani b with VLT/SPHERE
• Evolutionary models for ultracool dwarfs
• Results from The COPAINS Pilot Survey: four new brown dwarfs and a high companion detection rate for accelerating stars
• GRAVITY K-band spectroscopy of HD 206893 B: brown dwarf or exoplanet
• Towards Robust Atmospheric Retrieval on Cloudy L Dwarfs: The Impact of Thermal and Abundance Profile Assumptions
• A scaled-up planetary system around a supernova progenitor
• A dusty benchmark brown dwarf near the ice line of HD 72946
• Surveying Nearby Brown Dwarfs with HGCA: Direct Imaging Discovery of a Faint, High-Mass Brown Dwarf Orbiting HD 176535 A
• Precise dynamical masses of new directly imaged companions from combining relative astrometry, radial velocities, and Hipparcos-Gaia eDR3 accelerations
• A low-mass companion desert among intermediate-mass visual binaries: The scaled-up counterpart to the brown dwarf desert
• The ExoGRAVITY project: using single mode interferometry to characterize exoplanets

Cited by in corpus (7)

• Four-of-a-kind? Comprehensive atmospheric characterisation of the HR 8799 planets with VLTI/GRAVITY
• The ExoGRAVITY survey: A K-band spectral library of giant exoplanet and brown dwarf companions
• Distinct Rotational Evolution of Giant Planets and Brown Dwarf Companions
• SCExAO/CHARIS and Gaia Direct Imaging and Astrometric Discovery of a Superjovian Planet 3--4 lambda/D from the Accelerating Star HIP 54515
• OASIS Survey Direct Imaging and Astrometric Discovery of HIP 71618 B: A Substellar Companion Suitable for the Roman Coronagraph Technology Demonstration
• Spectral analysis of two directly imaged benchmark L dwarf companions at the stellar-substellar boundary
• Direct Images of CO2 Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk