Project 1640 Observations of Brown Dwarf GJ 758 B: Near-Infrared Spectrum and Atmospheric Modeling

Abstract

The nearby Sun-like star GJ 758 hosts a cold substellar companion, GJ 758 B, at a projected separation of $\lesssim$30 AU, previously detected in high-contrast multi-band photometric observations. In order to better constrain the companion's physical characteristics, we acquired the first low-resolution ($R\sim 50$) near-infrared spectrum of it using the high-contrast hyperspectral imaging instrument Project 1640 on Palomar Observatory's 5-m Hale telescope. We obtained simultaneous images in 32 wavelength channels covering the $Y$, $J$, and $H$ bands ($\sim$952-1770 nm), and used data processing techniques based on principal component analysis to efficiently subtract chromatic background speckle-noise. GJ 758 B was detected in four epochs during 2013 and 2014. Basic astrometric measurements confirm its apparent northwest trajectory relative to the primary star, with no clear signs of orbital curvature. Spectra of SpeX/IRTF observed T dwarfs were compared to the combined spectrum of GJ 758 B, with ${\chi }^2$ minimization suggesting a best fit for spectral type T7.0$\pm$1.0, but with a shallow minimum over T5-T8. Fitting of synthetic spectra from the BT-Settl13 model atmospheres gives an effective temperature $T_{\text{eff}}=741\pm 25$ K and surface gravity $\log g=4.3\pm 0.5$ dex (cgs). Our derived best-fit spectral type and effective temperature from modeling of the low-resolution spectrum suggest a slightly earlier and hotter companion than previous findings from photometric data, but do not rule out current results, and confirm GJ 758 B as one of the coolest sub-stellar companions to a Sun-like star to date.

arXiv commentAccepted for publication in ApJ, 13 pages, 11 figures v2 updated with minor edits from corrected proofs

References in corpus (42)

• Validation of the new Hipparcos reduction
• Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 20945
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Images of a fourth planet orbiting HR 8799
• A giant planet imaged in the disk of the young star Beta Pictoris
• Ages for illustrative field stars using gyrochronology: viability, limitations and errors
• Detection and Characterization of Exoplanets and Disks using Projections on Karhunen-Loeve Eigenimages
• The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
• The Gemini Planet Imager: First Light
• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• The Geneva-Copenhagen Survey of the Solar neighbourhood III. Improved distances, ages, and kinematics
• A Unified Near Infrared Spectral Classification Scheme for T Dwarfs
• Neglected Clouds in T and Y Dwarf Atmospheres
• The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)
• Structure and Evolution of Nearby Stars with Planets II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
• Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime
• Atmospheric Parameters of Field L and T Dwarfs
• Direct Imaging and Spectroscopy of a Planetary Mass Candidate Companion to a Young Solar Analog
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• PALM-3000: Exoplanet Adaptive Optics for the 5-meter Hale Telescope
• A New High Contrast Imaging Program at Palomar Observatory
• Discovery of the Coldest Imaged Companion of a Sun-Like Star
• Formation of Giant Planets by Disk Instability on Wide Orbits Around Protostars with Varied Masses
• Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy
• 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
• Confirmation of the planet around HD 95086 by direct imaging
• Direct Imaging and Spectroscopy of a Candidate Companion Below/Near the Deuterium-Burning Limit In The Young Binary Star System, ROXs 42B
• First light of the VLT planet finder SPHERE. I. Detection and characterization of the sub-stellar companion GJ 758 B
• Astrometry and Photometry with Coronagraphs
• Near-Infrared Multi-Band Photometry of the Substellar Companion GJ 758 B
• Accurate Astrometry and Photometry of Saturated and Coronagraphic Point Spread Functions
• The Kappa Andromedae System: New Constraints on the Companion Mass, System Age & Further Multiplicity
• The TRENDS High-Contrast Imaging Survey. V. Discovery of an Old and Cold Benchmark T-dwarf Orbiting the Nearby G-star HD 19467
• Discovery of Seven Companions to Intermediate Mass Stars with Extreme Mass Ratios in the Scorpius-Centaurus Association
• A Data Cube Extraction Pipeline for a Coronagraphic Integral Field Spectrograph
• Direct Spectrum of the Benchmark T dwarf HD 19467 B
• High-Contrast 3.8 Micron Imaging Of The Brown Dwarf/Planet-Mass Companion to GJ 758
• S4: A Spatial-Spectral model for Speckle Suppression
• Electric Field Conjugation with the Project 1640 coronagraph
• Spectral Typing of Late Type Stellar Companions to Young Stars from Low Dispersion Near-Infrared Integral Field Unit Data
• A New Method for Characterizing Very-Low-Mass Companions with Low Resolution Near-Infrared Spectroscopy

Cited by in corpus (8)

• Population-Level Eccentricity Distributions of Imaged Exoplanets and Brown Dwarf Companions: Dynamical Evidence for Distinct Formation Channels
• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• Understanding the Impacts of Stellar Companions on Planet Formation and Evolution: A Survey of Stellar and Planetary Companions within 25 pc
• The GJ 504 system revisited. Combining interferometric, radial velocity, and high contrast imaging data
• Orbit and Dynamical Mass of the Late-T Dwarf Gl 758 B
• The Hawaii Infrared Parallax Program. V. New T-Dwarf Members and Candidate Members of Nearby Young Moving Groups
• Improving dynamical mass constraints for intermediate-period substellar companions using Gaia DR2
• A new statistical method for characterizing the atmospheres of extrasolar planets