Deep Thermal Infrared Imaging of HR 8799 bcde: New Atmospheric Constraints and Limits on a Fifth Planet

Abstract

We present new $L^{\prime }$ (3.8 $\mu m$) and Br-$\alpha$ (4.05 $\mu m$) data and reprocessed archival $L^{\prime }$ data for the young, planet-hosting star HR 8799 obtained with Keck/NIRC2, VLT/NaCo and Subaru/IRCS. We detect all four HR 8799 planets in each dataset at a moderate to high signal-to-noise (SNR $\gtrsim$ 6-15). We fail to identify a fifth planet, "HR 8799 f", at $r$ $<$ 15 $AU$ at a 5-$\sigma$ confidence level: one suggestive, marginally significant residual at 0.2" is most likely a PSF artifact. Assuming companion ages of 30 $Myr$ and the Baraffe (Spiegel \& Burrows) planet cooling models, we rule out an HR 8799 f with mass of 5 $M_J$ (7 $M_J$), 7 $M_J$ (10 $M_J$), and 12 $M_J$ (13 $M_J$) at $r_{proj}$ $\sim$ 12 $AU$, 9 $AU$, and 5 $AU$, respectively. All four HR 8799 planets have red early T dwarf-like $L^{\prime }$ - [4.05] colors, suggesting that their SEDs peak in between the $L^{\prime }$ and $M^{\prime }$ broadband filters. We find no statistically significant difference in HR 8799 cde's colors. Atmosphere models assuming thick, patchy clouds appear to better match HR 8799 bcde's photometry than models assuming a uniform cloud layer. While non-equilibrium carbon chemistry is required to explain HR 8799 bc's photometry/spectra, evidence for it from HR 8799 de's photometry is weaker. Future, deep IR spectroscopy/spectrophotometry with the Gemini Planet Imager, SCExAO/CHARIS, and other facilities may clarify whether the planets are chemically similar or heterogeneous.

18 pages, 6 Tables, and 9 Figures. Fig. 1a is the key figure. Accepted for publication in ApJ

References in corpus (13)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• The Gemini Planet Imager: First Light
• Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
• Fundamental limitations of high contrast imaging set by small sample statistics
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• The Gemini Deep Planet Survey -- GDPS
• Direct Imaging and Spectroscopy of a Planetary Mass Candidate Companion to a Young Solar Analog
• The Palomar/Keck Adaptive Optics Survey of Young Solar Analogs: Evidence for a Universal Companion Mass Function
• Discovery of a wide companion near the deuterium burning mass limit in the Upper Scorpius association
• Confidence Level and Sensitivity Limits in High Contrast Imaging
• New Evidence for a Substellar Luminosity Problem: Dynamical Mass for the Brown Dwarf Binary Gl 417BC
• Near-Infrared Detection and Characterization of the Exoplanet HD 95086 b with the Gemini Planet Imager
• A First-Look Atmospheric Modeling Study of the Young Directly-Imaged Planet-Mass Companion, ROXs 42Bb

Cited by in corpus (37)

• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• Simultaneous Detection of Water, Methane and Carbon Monoxide in the Atmosphere of Exoplanet HR8799b
• Recovery of the Candidate Protoplanet HD 100546 b with Gemini/NICI and Detection of Additional (Planet-Induced?) Disk Structure at Small Separations
• Reconnaissance of the HR 8799 Exosolar System II: Astrometry and Orbital Motion
• No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy Orbital architecture analysis with PyAstrOFit
• Detection and Bulk Properties of the HR 8799 Planets with High Resolution Spectroscopy
• Direct imaging discovery of a super-Jovian around the young Sun-like star AF Leporis
• Direct Imaging and Astrometric Detection of a Gas Giant Planet Orbiting an Accelerating Star
• Sulfur Hazes in Giant Exoplanet Atmospheres: Impacts on Reflected Light Spectra
• Direct Imaging Discovery and Dynamical Mass of a Substellar Companion Orbiting an Accelerating Hyades Sun-like Star with SCExAO/CHARIS
• Deep exploration of the planets HR 8799 b, c, and d with moderate resolution spectroscopy
• On the Composition of Young, Directly Imaged Giant Planets
• The LEECH Exoplanet Imaging Survey. Further constraints on the planet architecture of the HR 8799 system
• SCExAO/CHARIS Direct Imaging Discovery of a 20 au Separation, Low-Mass Ratio Brown Dwarf Companion to an Accelerating Sun-like Star
• Four-of-a-kind? Comprehensive atmospheric characterisation of the HR 8799 planets with VLTI/GRAVITY
• Spectral and orbital characterisation of the directly imaged giant planet HIP 65426 b
• On the Chemical Abundance of HR 8799 and the Planet c
• Direct imaging of sub-Jupiter mass exoplanets with James Webb Space Telescope coronagraphy
• Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-Resolution Data
• Orbital and dynamical analysis of the system around HR 8799. New astrometric epochs from VLT/SPHERE and LBT/LUCI
• An exact, generalised Laplace resonance in the HR 8799 planetary system
• Atmospheric Monitoring and Precise Spectroscopy of the HR 8799 Planets with SCExAO/CHARIS
• Dynamical Mass of the Exoplanet Host Star HR 8799
• JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO${}_2$ in the HR 8799 and 51 Eri Exoplanets' Atmospheres
• Deep orbital search for additional planets in the HR 8799 system
• Direct-imaging Discovery of a Substellar Companion Orbiting the Accelerating Variable Star, HIP 39017
• 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
• The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas
• The post-main-sequence fate of the HR 8799 planetary system
• Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with Extremely Large Telescopes
• A Unified Spectroscopic and Photometric Model to Infer Surface Inhomogeneity: Application to Luhman 16B
• Applying a temporal systematics model to vector Apodizing Phase Plate coronagraphic data: TRAP4vAPP
• PACOME: Optimal multi-epoch combination of direct imaging observations for joint exoplanet detection and orbit estimation
• The mid-infrared spectrum of $\beta$ Pictoris b. First VLTI/MATISSE interferometric observations of an exoplanet
• L-band Integral Field Spectroscopy of the HR 8799 Planetary System