Orbit and Dynamical Mass of the Late-T Dwarf Gl 758 B

Abstract

Gl 758 B is a late-T dwarf orbiting a metal-rich Sun-like star at a projected separation of $\rho$ $\approx$ 1.6" (25 AU). We present four epochs of astrometry of this system with NIRC2 at Keck Observatory spanning 2010 to 2017 together with 630 radial velocities (RVs) of the host star acquired over the past two decades from McDonald Observatory, Keck Observatory, and the Automated Planet Finder at Lick Observatory. The RVs reveal that Gl 758 is accelerating with an evolving rate that varies between 2-5 m s${}^{-1}$ yr${}^{-1}$, consistent with the expected influence of the imaged companion Gl 758 B. A joint fit of the RVs and astrometry yields a dynamical mass of 42${}_{-7}^{+19}$ M${}_{\mathrm{Jup}}$ for the companion with a robust lower limit of 30.5 M${}_{\mathrm{Jup}}$ at the 4-$\sigma$ level. Gl 758 B is on an eccentric orbit ($e$ = 0.26-0.67 at 95% confidence) with a semimajor axis of $a$ = $21.1_{-1.3}^{+2.7}$ AU and an orbital period of $P$ = $96_{-9}^{+21}$ yr, which takes it within $\approx$9 AU from its host star at periastron passage. Substellar evolutionary models generally underpredict the mass of Gl 758 B for nominal ages of 1-6 Gyr that have previously been adopted for the host star. This discrepancy can be reconciled if the system is older---which is consistent with activity indicators and recent isochrone fitting of the host star---or alternatively if the models are systematically overluminous by $\approx$0.1-0.2 dex. Gl 758 B is currently the lowest-mass directly imaged companion inducing a measured acceleration on its host star. In the future, bridging RVs and high-contrast imaging with the next generation of extremely large telescopes and space-based facilities will open the door to the first dynamical mass measurements of imaged exoplanets.

AJ, accepted

References in corpus (13)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• An ancient extrasolar system with five sub-Earth-size planets
• Planets Around Low-Mass Stars (PALMS). IV. The Outer Architecture of M Dwarf Planetary Systems
• Abundances in the Local Region II: F, G and K Dwarfs and Subgiants
• Characterizing 51 Eri b from 1-5 $\mu$m: a partly-cloudy exoplanet
• Keck Laser Guide Star Adaptive Optics Monitoring of 2MASS J1534-2952AB: First Dynamical Mass Determination of a Binary T Dwarf
• Three Super-Earths Orbiting HD 7924
• New Evidence for a Substellar Luminosity Problem: Dynamical Mass for the Brown Dwarf Binary Gl 417BC
• Dynamical Mass of GJ 802B: a brown dwarf in a triple system
• Planets Around Low-Mass Stars (PALMS). VI. Discovery of a Remarkably Red Planetary-Mass Companion to the AB Dor Moving Group Candidate 2MASS J22362452+4751425
• Planets Around Low-Mass Stars (PALMS). V. Age-Dating Low-Mass Companions to Members and Interlopers of Young Moving Groups

Cited by in corpus (42)

• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• The SPHERE infrared survey for exoplanets (SHINE). III. The demographics of young giant exoplanets below 300 au with SPHERE
• Population-Level Eccentricity Distributions of Imaged Exoplanets and Brown Dwarf Companions: Dynamical Evidence for Distinct Formation Channels
• Precise Dynamical Masses of Directly Imaged Companions from Relative Astrometry, Radial Velocities, and Hipparcos-Gaia DR2 Accelerations
• 3-D selection of 167 sub-stellar companions to nearby stars
• Understanding the Impacts of Stellar Companions on Planet Formation and Evolution: A Survey of Stellar and Planetary Companions within 25 pc
• Impact of a new H/He equation of state on the evolution of massive brown dwarfs. New determination of the hydrogen burning limit
• Direct Imaging and Astrometric Detection of a Gas Giant Planet Orbiting an Accelerating Star
• Improved Dynamical Masses for Six Brown Dwarf Companions Using Hipparcos and Gaia EDR3
• Obliquity Constraints on an Extrasolar Planetary-Mass Companion
• Rotation Periods, Inclinations, and Obliquities of Cool Stars Hosting Directly Imaged Substellar Companions: Spin-Orbit Misalignments are Common
• Weighing the Darkness: Astrometric Mass Measurement of Hidden Stellar Companions using Gaia
• A Dynamical Mass of $70\pm 5$ Jupiter Masses for Gliese 229B, the First T Dwarf
• Dynamical Masses of Eps Ind B and C: Two Massive Brown Dwarfs at the Edge of the Stellar-Substellar Boundary
• WISE J072003.20-084651.2B Is A Massive T Dwarf
• The Hawaii Infrared Parallax Program. V. New T-Dwarf Members and Candidate Members of Nearby Young Moving Groups
• Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-Dwarf Companion in the Hyades
• The Hawaii Infrared Parallax Program. III. 2MASS J0249-0557 c: A Wide Planetary-mass Companion to a Low-mass Binary in the beta Pic Moving Group
• Dynamical Mass of the Young Substellar Companion HD 984 B
• Uniform Forward-Modeling Analysis of Ultracool Dwarfs. II. Atmospheric Properties of 55 Late-T Dwarfs
• Improving dynamical mass constraints for intermediate-period substellar companions using Gaia DR2
• Uniform Forward-Modeling Analysis of Ultracool Dwarfs. I. Methodology and Benchmarking
• The Orbital Eccentricities of Directly Imaged Companions Using Observable-Based Priors: Implications for Population-level Distributions
• Frequency of Planets in Binaries
• Supervised Machine Learning for Intercomparison of Model Grids of Brown Dwarfs: Application to GJ 570D and the Epsilon Indi B Binary System
• Spectral and atmospheric characterisation of a new benchmark brown dwarf HD13724B
• Orbital and spectral characterization of the benchmark T-type brown dwarf HD 19467B
• The McDonald Accelerating Stars Survey (MASS): White Dwarf Companions Accelerating the Sun-like Stars 12 Psc and HD 159062
• Dynamical Mass of the Exoplanet Host Star HR 8799
• A dusty benchmark brown dwarf near the ice line of HD 72946
• The McDonald Accelerating Stars Survey (MASS): Discovery of a Long-Period Substellar Companion Orbiting the Old Solar Analog HD 47127
• Precise dynamical masses of new directly imaged companions from combining relative astrometry, radial velocities, and Hipparcos-Gaia eDR3 accelerations
• Dynamical Mass of the Young Brown Dwarf Companion PZ Tel B
• Dynamical masses for two M1 + mid-M dwarf binaries monitored during the SPHERE-SHINE survey
• Multi-Epoch VLBI of L Dwarf Binary 2MASS J0746+2000AB: Precise Mass Measurements and Confirmation of Radio Emission from Both Components
• Combining high contrast imaging and radial velocities to constrain the planetary architecture of nearby stars
• The TRENDS High-contrast Imaging Survey. VIII. Compendium of Benchmark Objects
• The McDonald Accelerating Stars Survey (MASS): Architecture of the Ancient Five-Planet Host System Kepler-444
• Dynamical masses for the Pleiades binary system HII-2147
• Dynamical masses across the Hertzsprung-Russell diagram
• Informed systematic method to identify variable mid and late-T dwarfs
• Where to find over-massive brown dwarfs: new benchmark systems for binary evolution