The McDonald Accelerating Stars Survey (MASS): Discovery of a Long-Period Substellar Companion Orbiting the Old Solar Analog HD 47127

Abstract

Brown dwarfs with well-determined ages, luminosities, and masses provide rare but valuable tests of low-temperature atmospheric and evolutionary models. We present the discovery and dynamical mass measurement of a substellar companion to HD 47127, an old ($\approx$7-10 Gyr) G5 main sequence star with a mass similar to the Sun. Radial velocities of the host star with the Harlan J. Smith Telescope uncovered a low-amplitude acceleration of 1.93 $\pm$ 0.08 m s${}^{-1}$ yr${}^{-1}$ based on 20 years of monitoring. We subsequently recovered a faint ($\Delta H$=13.14 $\pm$ 0.15 mag) co-moving companion at 1.95${}^{\prime \prime }$ (52 AU) with follow-up Keck/NIRC2 adaptive optics imaging. The radial acceleration of HD 47127 together with its tangential acceleration from Hipparcos and Gaia EDR3 astrometry provide a direct measurement of the three-dimensional acceleration vector of the host star, enabling a dynamical mass constraint for HD 47127 B (67.5-177 $M_{\mathrm{Jup}}$ at 95% confidence) despite the small fractional orbital coverage of the observations. The absolute $H$-band magnitude of HD 47127 B is fainter than the benchmark T dwarfs HD 19467 B and Gl 229 B but brighter than Gl 758 B and HD 4113 C, suggesting a late-T spectral type. Altogether the mass limits for HD 47127 B from its dynamical mass and the substellar boundary imply a range of 67-78 $M_{\mathrm{Jup}}$ assuming it is single, although a preference for high masses of $\approx$100 $M_{\mathrm{Jup}}$ from dynamical constraints hints at the possibility that HD 47127 B could itself be a binary pair of brown dwarfs or that another massive companion resides closer in. Regardless, HD 47127 B will be an excellent target for more refined orbital and atmospheric characterization in the future.

Accepted to ApJ Letters

References in corpus (16)

• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• On the Luminosity of Young Jupiters
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres
• Planets Around Low-Mass Stars (PALMS). IV. The Outer Architecture of M Dwarf Planetary Systems
• Population-Level Eccentricity Distributions of Imaged Exoplanets and Brown Dwarf Companions: Dynamical Evidence for Distinct Formation Channels
• Abundances in the Local Region II: F, G and K Dwarfs and Subgiants
• Keck Laser Guide Star Adaptive Optics Monitoring of 2MASS J1534-2952AB: First Dynamical Mass Determination of a Binary T Dwarf
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• New Evidence for a Substellar Luminosity Problem: Dynamical Mass for the Brown Dwarf Binary Gl 417BC
• SCExAO/CHARIS Direct Imaging Discovery of a 20 au Separation, Low-Mass Ratio Brown Dwarf Companion to an Accelerating Sun-like Star
• BAFFLES: Bayesian Ages for Field Lower-Mass Stars
• Evolutionary models for ultracool dwarfs
• 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

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• Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-Dwarf Companion in the Hyades
• Dynamical Mass of the Young Substellar Companion HD 984 B
• The Active Chromospheres of Lithium-Rich Red Giant Stars
• Surveying Nearby Brown Dwarfs with HGCA: Direct Imaging Discovery of a Faint, High-Mass Brown Dwarf Orbiting HD 176535 A
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