$L$-band Spectra of Young Brown Dwarfs

Abstract

We present a $L$-band (2.98--3.96$\mu$m) spectroscopic study of 8 young L dwarfs with spectral types ranging from L2 to L7. Our spectra ($\lambda /\Delta \lambda \approx$ 250 to 600) were collected using the Gemini Near-InfraRed Spectrograph. We first examine the young $L$-band spectral sequence, most notably analyzing the evolution of the $Q$-branch of methane absorption feature at 3.3 $\mu$m. We find the $Q$-branch feature first appears between L3 and L6, as previously seen in older field dwarfs. Secondly, we analyze how well various atmospheric models reproduce the $L$-band and published near-IR (0.7--2.5 $\mu$m) spectra of our objects by fitting five different grids of model spectra to the data. Best-fit parameters for the combined near-IR and $L$-band data are compared to best-fit parameters for just the near-IR data, isolating the impact that the addition of the $L$-band has on the results. This addition notably causes a $\sim$100 K drop in the best-fit effective temperature. Also, when clouds and a vertical mixing rate ($K_{\mathrm{zz}}$) are included in the models, thick clouds and higher $K_{\mathrm{zz}}$ values are preferred. Five of our objects also have previously published effective temperatures and surface gravities derived using evolutionary models, age estimates, and bolometric luminosities. Comparing model spectra matching these parameters to our spectra, we find disequilibrium chemistry and clouds are needed to match these published effective temperatures. Three of these objects are members of AB Dor, allowing us to show the temperature dependence of the $Q$-branch of methane.

arXiv comment26 pages, 19 figures, Accepted for publication in MNRAS

References in corpus (58)

• The chemical composition of the Sun
• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• A Method of Correcting Near-Infrared Spectra for Telluric Absorption
• Models of Stars, Brown Dwarfs and Exoplanets
• The NASA Exoplanet Archive: Data and Tools for Exoplanet Research
• Solar Chemical Abundances Determined with a CO5BOLD 3D Model Atmosphere
• Precipitating Condensation Clouds in Substellar Atmospheres
• Spectral Irradiance Calibration in the Infrared. XIV: the Absolute Calibration of 2MASS
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope
• A probable giant planet imaged in the Beta Pictoris disk
• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• 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
• Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime
• A Near-Infrared Spectroscopic Study of Young Field Ultracool Dwarfs
• Atmospheric Parameters of Field L and T Dwarfs
• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• BANYAN. II. Very Low Mass and Substellar Candidate Members to Nearby, Young Kinematic Groups With Previously Known Signs of Youth
• The Brown Dwarf Kinematics Project (BDKP). III. Parallaxes for 70 Ultracool Dwarfs
• Weather on Other Worlds. II. Survey Results: Spots Are Ubiquitous on L and T Dwarfs
• Population Properties of Brown Dwarf Analogs to Exoplanets
• Giant Planet Companion to 2MASSW J1207334-393254
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• The Extremely Red, Young L Dwarf PSO J318-22: A Free-Floating Planetary-Mass Analog to Directly Imaged Young Gas-Giant Planets
• Distances, Luminosities, and Temperatures of the Coldest Known Substellar Objects
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• Discovery of a Very Young Field L Dwarf, 2MASS J01415823-4633574
• A Patchy Cloud Model for the L to T Dwarf Transition
• The Mauna Kea Observatories Near-Infrared Filter Set. III. Isophotal Wavelengths and Absolute Calibration
• Cloudless atmospheres for L/T dwarfs and extra-solar giant planets
• An Infrared/X-ray Survey for New Members of the Taurus Star-Forming Region
• Model atmospheres for massive gas giants with thick clouds: Application to the HR 8799 planets and predictions for future detections
• Discovery of Two Nearby, Peculiar L Dwarfs from the 2MASS Proper Motion Survey: Young or Metal-Rich?
• 2MASSJ035523.51+113337.4: A Young, Dusty, Nearby, Isolated Brown Dwarf Resembling A Giant Exoplanet
• First Light LBT AO Images of HR 8799 bcde at 1.65 and 3.3 Microns: New Discrepancies between Young Planets and Old Brown Dwarfs
• Dust in brown dwarfs and extra-solar planets II. Cloud formation for cosmologically evolving abundances
• Photometry and Proper Motions of M, L, and T Dwarfs from the Pan-STARRS1 3$\pi$ Survey
• Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158
• 1 to 2.4 micron Near-IR spectrum of the Giant Planet $\beta$ Pictoris b obtained with the Gemini Planet Imager
• 2MASS J05185995-2828372: Discovery of an Unresolved L/T Binary
• 3.6-7.9 um Photometry of L and T Dwarfs and the Prevalence of Vertical Mixing in their Atmospheres
• Physical Properties of Young Brown Dwarfs and Very Low-Mass Stars Inferred from High-Resolution Model Spectra
• The Onset of Methane in L Dwarfs
• A Kine-Chemical Investigation of the AB Dor Moving Group "Stream"
• Discovery of an Unusually Red L-type Brown Dwarf
• The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 dwarfs with UKIRT
• Magellan Adaptive Optics first-light observations of the exoplanet $\beta$ Pic b. I. Direct imaging in the far-red optical with MagAO+VisAO and in the near-IR with NICI
• WISEP J004701.06+680352.1: An intermediate surface gravity, dusty brown dwarf in the AB Dor Moving Group
• Discovery of a Young L Dwarf Binary, SDSS J224953.47+004404.6AB
• WISEA J114724.10-204021.3: A Free-Floating Planetary Mass Member of the TW Hya Association
• Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
• Variability of the Lowest Mass Objects in the AB Doradus Moving Group
• Cloudless atmospheres for young low-gravity substellar objects
• The Radial and Rotational Velocities of PSO J318.5338$-$22.8603, a Newly Confirmed Planetary-Mass Member of the $\beta$ Pictoris Moving Group
• New constraints on the formation and settling of dust in the atmospheres of young M and L dwarfs
• The Nearest Isolated Member of the TW Hydrae Association is a Giant Planet Analog
• Methane in Analogs of Young Directly Imaged Exoplanets
• Infrared and kinematic properties of the substellar object G 196-3B

Cited by in corpus (2)

• JWST/NIRSpec Observations of the Planetary Mass Companion TWA 27B
• Near-infrared spectroscopic characterisation of Gaia ultra-cool dwarf candidates; Spectral types and peculiarities