The Brown Dwarf Kinematics Project (BDKP). V. Radial and Rotational Velocities of T Dwarfs from Keck/NIRSPEC High-Resolution Spectroscopy

Abstract

We report multi-epoch radial velocities, rotational velocities, and atmospheric parameters for 37 T-type brown dwarfs observed with Keck/NIRSPEC. Using a Markov Chain Monte Carlo forward-modeling method, we achieve median precisions of 0.5 km s${}^{-1}$ and 0.9 km s${}^{-1}$ for radial and rotational velocities, respectively. All of the T dwarfs in our sample are thin disk brown dwarfs. We confirm previously reported moving group associations for four T dwarfs. However, the lack of spectral indicators of youth in two of these sources suggests that these are chance alignments. We confirm two previously un-resolved binary candidates, the T0+T4.5 2MASS J11061197+2754225 and the L7+T3.5 2MASS J21265916+7617440, with orbital periods of 4 yr and 12 yr, respectively. We find a kinematic age of 3.5$\pm$0.3 Gyr for local T dwarfs, consistent with nearby late-M dwarfs (4.1$\pm$0.3 Gyr). Removal of thick disk L dwarfs in the local ultracool dwarf sample gives a similar age for L dwarfs (4.2$\pm$0.3 Gyr), largely resolving the local L dwarf age anomaly. The kinematic ages of local late-M, L, and T dwarfs can be accurately reproduced with population simulations incorporating standard assumptions of the mass function, star formation rate, and brown dwarf evolutionary models. A kinematic dispersion break is found at the L4$-$L6 subtypes, likely reflecting the terminus of the stellar Main Sequence. We provide a compilation of precise radial velocities for 172 late-M, L, and T dwarfs within $\sim$20 pc of the Sun.

84 pages, 33 figures. Accepted for publication in ApJS

References in corpus (60)

• The NumPy array: a structure for efficient numerical computation
• Cosmic Star Formation History
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• galpy: A Python Library for Galactic Dynamics
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Large-scale magnetic topologies of late M dwarfs
• Measuring the rotation period distribution of field M-dwarfs with Kepler
• 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
• On the local dark matter density
• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• Chromospheric Activity, Rotation, and Rotational Braking in M and L Dwarfs
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
• Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition
• Activity and Kinematics of Ultracool Dwarfs Including An Amazing Flare Observation
• Subtle Signatures of Multiplicity in Late-type Dwarf Spectra: The Unresolved M8.5 + T5 Binary 2MASS J03202839-0446358
• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• Discovery of 11 New T Dwarfs in the Two Micron All-Sky Survey, Including a Possible L/T Transition Binary
• A search for binary systems among the nearest L dwarfs
• A Cross-Match of 2MASS and SDSS: Newly-Found L and T Dwarfs and an Estimate of the Space Densitfy of T Dwarfs
• SpeX Spectroscopy of Unresolved Very Low Mass Binaries. II. Identification of Fourteen Candidate Binaries with Late-M/Early-L and T Dwarf Components
• Discovery of a wide planetary-mass companion to the young M3 star GU Psc
• The Viewing Geometry of Brown Dwarfs Influences Their Observed Colours and Variability Properties
• Flux calibration of medium-resolution spectra from 300 nm to 2500 nm: Model reference spectra and telluric correction
• Doppler Imaging of Exoplanets and Brown Dwarfs
• Discovery of a T Dwarf Binary with the Largest Known J-Band Flux Reversal
• Discovery of new nearby L and late-M dwarfs at low Galactic latitude from the DENIS database
• Observations of Disequilibrium CO Chemistry in the Coldest Brown Dwarfs
• The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs
• Exploring the Local Milky Way: M Dwarfs as Tracers of Galactic Populations
• The age-velocity dispersion relation of the Galactic discs from LAMOST-Gaia data
• The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs
• Exploring the age dependent properties of M and L dwarfs using Gaia and SDSS
• The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 dwarfs with UKIRT
• Space Velocities of L- and T-type Dwarfs
• Multiepoch Radial Velocity Observations of L Dwarfs
• Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-Cool Dwarfs
• Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project
• The Young L Dwarf 2MASS J11193254-1137466 is a Planetary-Mass Binary
• Evaluating Rotation Periods of M Dwarfs Across the Ages
• Variability of the Lowest Mass Objects in the AB Doradus Moving Group
• Proper motions of field L and T dwarfs
• WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun
• A 3D Search for Companions to 12 Nearby M-Dwarfs
• Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs
• A Spectroscopic Binary at the M/L Transition
• The Hawaii Infrared Parallax Program. V. New T-Dwarf Members and Candidate Members of Nearby Young Moving Groups
• CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs
• L and T dwarfs in the Hyades and Ursa Major moving groups
• Weather on Other Worlds. III. A Survey for T Dwarfs with High Amplitude Optical Variability
• 2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary
• The ages of L dwarfs
• A Method To Remove Fringes From Images Using Wavelets
• New ultracool dwarf neighbours within 20pc from Gaia DR2
• Low-resolution optical spectra of ultracool dwarfs with OSIRIS/GTC
• Optical Spectra of Ultracool Dwarfs with the Southern African Large Telescope
• Astrometric orbits of spectral binary brown dwarfs I: Massive T dwarf companions to 2M1059$-$21 and 2M0805$+$48
• The Effect of Atmospheric Cooling on the Vertical Velocity Dispersion and Density Distribution of Brown Dwarfs
• Individual Dynamical Masses of DENIS J063001.4$-$184014AB Reveal A Likely Young Brown Dwarf Triple
• Globular cluster absolute ages from cooling brown dwarfs

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