Probing Late-type T dwarf J-H Color Outliers for Signs of Age

Abstract

We present the results of a Keck/NIRSPEC follow-up survey of thirteen late-type T dwarfs (T6-T9), twelve of which have unusually red or blue J-H colors. Previous work suggests that J-H color outliers may represent the high-gravity, low-metallicity (old) and low-gravity, solar-metallicity (young) extremes of the late-type T dwarf population. We use medium-resolution Y- and H-band spectroscopy to probe regions of T dwarf atmospheres that are more sensitive to gravity and metallicity variations than the J band. We find that the spectral morphologies of our sample are largely homogeneous, with peak-normalized, Y- and H-band morphologies consistent with spectral standards. However, three objects stand out as potentially old, with overluminous Y-band spectra compared to their respective spectral standards, and a fourth object stands out as potentially young, with an underluminous Y band. Of these four objects, three have been previously identified as potential metallicity/gravity outliers, including the one object in our sample with a normal J-H color. We fit publicly available atmospheric model grids to our spectra and find that the best-fit physical parameters vary depending on the model used. As we continue to probe the characteristics of the late-T population, differences in synthetic spectra of ~10-20% in the blue wing of the Y band and ~45% at 1.65 microns, for the same physical parameters, must be reconciled. Further development and public availability of nonsolar metallicity models is also recommended. Future progress toward deciphering the impacts of gravity, metallicity, and variability in the late-type T dwarf population will also require high signal-to-noise, multiwavelength and multi-epoch photometry and spectroscopy.

arXiv commentaccepted to ApJ

References in corpus (91)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• Validation of the new Hipparcos reduction
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• A Non-Gray Theory of Extrasolar Giant Planets and Brown Dwarfs
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: the Effects of Temperature, Clouds, and Gravity
• Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I
• A Unified Near Infrared Spectral Classification Scheme for T Dwarfs
• Neglected Clouds in T and Y Dwarf Atmospheres
• Preliminary Parallaxes of 40 L and T Dwarfs from the U.S. Naval Observatory Infrared Astrometry Program
• The Spectra of T Dwarfs I: Near-Infrared Data and Spectral Classification
• The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)
• The Discovery of Y Dwarfs Using Data from the Wide-field Infrared Survey Explorer (WISE)
• L and T Dwarf Models and the L to T Transition
• Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function
• Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime
• Clouds and Chemistry: Ultracool Dwarf Atmospheric Properties from Optical and Infrared Colors
• A Near-Infrared Spectroscopic Study of Young Field Ultracool Dwarfs
• The NIRSPEC Brown Dwarf Spectroscopic Survey. I. Low-Resolution Near-Infrared Spectra
• The Brown Dwarf Kinematics Project (BDKP) I. Proper Motions and Tangential Velocities for a Large Sample of Late-type M, L and T Dwarfs
• Weather on Other Worlds. II. Survey Results: Spots Are Ubiquitous on L and T Dwarfs
• Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
• The Mauna Kea Observatories Near-Infrared Filter Set. I: Defining Optimal 1-5 $\mu$m Bandpasses
• A Patchy Cloud Model for the L to T Dwarf Transition
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets
• Large Amplitude Variations of an L/T Transition Brown Dwarf: Multi-Wavelength Observations of Patchy, High-Contrast Cloud Features
• Strong Brightness Variations Signal Cloudy-to-Clear Transition of Brown Dwarfs
• Activity and Kinematics of Ultracool Dwarfs Including An Amazing Flare Observation
• The First Substellar Subdwarf? Discovery of a Metal-poor L Dwarf with Halo Kinematics
• A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs
• Identifying Young Brown Dwarfs Using Gravity-Sensitive Spectral Features
• Mid-Infrared Photometry of Cold Brown Dwarfs: Diversity in Age, Mass and Metallicity
• The Spectra of T Dwarfs. II. Red Optical Data
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• Atmospheric dynamics of brown dwarfs and directly imaged giant planets
• The Dependence of Brown Dwarf Radii on Atmospheric Metallicity and Clouds: Theory and Comparison with Observations
• The AllWISE Motion Survey and The Quest for Cold Subdwarfs
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• Brown Dwarf Photospheres are Patchy: A Hubble Space Telescope Near-infrared Spectroscopic Survey Finds Frequent Low-level Variability
• The discovery of a very cool, very nearby brown dwarf in the Galactic plane
• New H2 collision-induced absorption and NH3 opacity and the spectra of the coolest brown dwarfs
• A Study of the Diverse T Dwarf Population Revealed by WISE
• Atmospheres from very low-mass stars to extrasolar planets
• Seventy six T dwarfs from the UKIDSS LAS: benchmarks, kinematics and an updated space density
• The discovery of an M4+T8.5 binary system
• Clouds in the Coldest Brown Dwarfs: FIRE Spectroscopy of Ross 458C
• Exploring the substellar temperature regime down to ~550K
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs II: Properties of 11 T-dwarfs
• Keck Laser Guide Star Adaptive Optics Monitoring of 2MASS J1534-2952AB: First Dynamical Mass Determination of a Binary T Dwarf
• Theoretical Spectral Models of T Dwarfs at Short Wavelengths and Their Comparison with Data
• Discovery of a Bright Field Methane (T-type) Brown Dwarf by 2MASS
• Physical and Spectral Characteristics of the T8 and Later-Type Dwarfs
• Finding benchmark brown dwarfs to probe the IMF as a function of time
• The Dynamical Mass and Three-Dimensional Orbit of HR7672B: A Benchmark Brown Dwarf with High Eccentricity
• Forty seven new T dwarfs from the UKIDSS Large Area Survey
• WISE Y Dwarfs As Probes of the Brown Dwarf-Exoplanet Connection
• The First Ultra-Cool Brown Dwarf Discovered by the Wide-field Infrared Survey Explorer
• Two Extraordinary Substellar Binaries at the T/Y Transition and the Y-Band Fluxes of the Coolest Brown Dwarfs
• The Y-Type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry and Near-Infrared Spectroscopy
• Near-infrared photometry of Y dwarfs: low ammonia abundance and the onset of water clouds
• WISE Brown Dwarf Binaries: The Discovery of a T5+T5 and a T8.5+T9 System
• A Comparison of Near-Infrared Photometry and Spectra for Y Dwarfs with a New Generation of Cool Cloudy Models
• Hip 63510C, Hip 73786B, and nine new isolated high proper motion T dwarf candidates from UKIDSS DR6 and SDSS DR7
• Nearby M, L, and T Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)
• The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs
• Keck Laser Guide Star Adaptive Optics Monitoring of the M8+L7 Binary LHS 2397aAB: First Dynamical Mass Benchmark at the L/T Transition
• Discovery of the benchmark metal poor T8 dwarf BD+01 2920B
• Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
• Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric properties
• Temperature Fluctuations as a Source of Brown Dwarf Variability
• The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey
• The Exemplar T8 Subdwarf Companion of Wolf 1130
• Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
• The First Detection of Photometric Variability in a Y Dwarf: WISE J140518.39+553421.3
• The Coldest Brown Dwarf (Or Free Floating Planet)?: The Y Dwarf WISE 1828+2650
• Blue not brown: UKIDSS T dwarfs with suppressed K-band flux
• New M, L, and T Dwarf Companions to Nearby Stars from the Wide-field Infrared Survey Explorer
• Discovery of the Y1 Dwarf WISE J064723.23-623235.5
• Observed Variability at 1um and 4um in the Y0 Brown Dwarf WISEP J173835.52+273258.9
• FIRE Spectroscopy of Five Late-type T Dwarfs Discovered with the Wide-field Infrared Survey Explorer
• Discovery of a new Y dwarf: WISE J030449.03-270508.3
• Wolf 1130: A Nearby Triple System Containing a Cool, Ultramassive White Dwarf
• The discovery of a T6.5 subdwarf
• Properties of the T8.5 Dwarf Wolf 940 B
• The discovery of the T8.5 dwarf UGPS J0521+3640
• Robust detection of quasi-periodic variability: A HAWKI mini survey of late T dwarfs
• Ultracool dwarf benchmarks with \emph{Gaia} primaries
• Four Faint T Dwarfs from the UKIRT Infrared Deep Sky Survey (UKIDSS) Southern Stripe
• The Brown-dwarf Atmosphere Monitoring (BAM) Project II: Multi-epoch monitoring of extremely cool brown dwarfs

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• Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs
• Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs
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