Moderate-Resolution $K$-Band Spectroscopy of the Substellar Companion VHS 1256 b

Abstract

We present moderate-resolution ($R\sim 4000$) $K$ band spectra of the planetary-mass companion VHS 1256 b. The data were taken with the OSIRIS integral field spectrograph at the W.M. Keck Observatory. The spectra reveal resolved molecular lines from H${}_2$O and CO. The spectra are compared to custom $PHOENIX$ atmosphere model grids appropriate for young, substellar objects. We fit the data using a Markov Chain Monte Carlo forward modeling method. Using a combination of our moderate-resolution spectrum and low-resolution, broadband data from the literature, we derive an effective temperature of 1240 K, with a range of 1200--1300 K, a surface gravity of $\log g=$ 3.25, with a range of 3.25--3.75 and a cloud parameter of $\log P_{cloud}=$ 6, with a range of 6.0--6.6. These values are consistent with previous studies, regardless of the new, larger system distance from GAIA EDR3 (22.2${}_{-1.2}^{+1.1}$ pc). We derive a C/O ratio of 0.590${}_{-0.354}^{+0.280}$ for VHS 1256b. Both our OSIRIS data and spectra from the literature are best modeled when using a larger 3 $\mu$m grain size for the clouds than used for hotter objects, consistent with other sources in the L/T transition region. VHS 1256 b offers an opportunity to look for systematics in the modeling process that may lead to the incorrect derivation of properties like C/O ratio in the high contrast regime.

arXiv comment16 pages, 10 figures. arXiv admin note: text overlap with arXiv:2009.08959

References in corpus (39)

• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• The NextGen Model Atmosphere grid for $3000\le \Teff \le 10000\K$
• The Limiting Effects of Dust in Brown Dwarf Model Atmospheres
• The effects of snowlines on C/O in planetary atmospheres
• The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics From 10-100 AU
• Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
• Imaging Extrasolar Giant Planets
• Clouds and Chemistry in the Atmosphere of Extrasolar Planet HR8799b
• Exoplanetary Atmospheres: Key Insights, Challenges and Prospects
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• An accurate, extensive, and practical line list of methane for the HITEMP database
• The SPHERE infrared survey for exoplanets (SHINE). III. The demographics of young giant exoplanets below 300 au with SPHERE
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• The Gemini NICI Planet-Finding Campaign: The Frequency of Planets around Young Moving Group Stars
• The NIRSPEC Ultracool Dwarf Radial Velocity Survey
• Simultaneous Detection of Water, Methane and Carbon Monoxide in the Atmosphere of Exoplanet HR8799b
• Discovery of a young planetary mass companion to the nearby M dwarf VHS J125601.92-125723.9
• 2MASSJ035523.51+113337.4: A Young, Dusty, Nearby, Isolated Brown Dwarf Resembling A Giant Exoplanet
• Stability of the directly imaged multiplanet system HR 8799: resonance and masses
• Confirmation of the planet around HD 95086 by direct imaging
• The International Deep Planet Survey II: The frequency of directly imaged giant exoplanets with stellar mass
• The 13O-rich atmosphere of a young accreting super-Jupiter
• A medium-resolution spectrum of the exoplanet HIP 65426 b
• Deep exploration of the planets HR 8799 b, c, and d with moderate resolution spectroscopy
• A Search for Variability in Exoplanet Analogues and Low-Gravity Brown Dwarfs
• Strong Near-Infrared Spectral Variability of the Young Cloudy L Dwarf Companion VHS J1256-1257 b
• Adaptive Optics imaging of VHS 1256-1257: A Low Mass Companion to a Brown Dwarf Binary System
• Hubble PanCET: An isothermal day-side atmosphere for the bloated gas-giant HAT-P-32Ab
• Retrieving the C and O Abundances of HR 7672~AB: a Solar-Type Primary Star with a Benchmark Brown Dwarf
• A Thermal Infrared Imaging Study of Very Low-Mass, Wide Separation Brown Dwarf Companions to Upper Scorpius Stars: Constraining Circumstellar Environments
• Heavy Element Enrichment of a Jupiter-mass Protoplanet as a Function of Orbital Location
• Methane in Analogs of Young Directly Imaged Exoplanets
• The 3-D Kinematics of the Orion Nebula Cluster: NIRSPEC-AO Radial Velocities of the Core Population
• Moderate-Resolution $K$-Band Spectroscopy of Substellar Companion $\kappa$ Andromedae b
• Detailed elemental abundances of binary stars: Searching for signatures of planet formation and atomic diffusion
• Supervised Machine Learning for Intercomparison of Model Grids of Brown Dwarfs: Application to GJ 570D and the Epsilon Indi B Binary System
• Characterizing and Improving the Data Reduction Pipeline for the Keck OSIRIS Integral Field Spectrograph
• The First Brown Dwarf/Planetary-Mass Object in the 32 Orionis Group
• Thermal Infrared Imaging and Atmospheric Modeling of VHS J125601.92-125723.9 b: Evidence for Moderately Thick Clouds and Equilibrium Carbon Chemistry in a Hierarchical Triple System

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