Investigating Trends in Atmospheric Compositions of Cool Gas Giant Planets Using Spitzer Secondary Eclipses

Abstract

We present new 3.6 and 4.5 micron secondary eclipse measurements for five cool (less than approximately 1000 K) transiting gas giant planets: HAT-P-15b, HAT-P-17b, HAT-P-18b, HAT-P-26b, and WASP-69b. We detect eclipses in at least one bandpass for all planets except HAT-P-15b. We confirm and refine the orbital eccentricity of HAT-P-17b, which is also the only planet in our sample with a known outer companion. We compare our measured eclipse depths in these two bands, which are sensitive to the relative abundances of methane versus carbon monoxide and carbon dioxide, respectively, to predictions from 1D atmosphere models for each planet. For planets with hydrogen-dominated atmospheres and equilibrium temperatures cooler than approximately 1000 K, this ratio should vary as a function of both atmospheric metallicity and the carbon-to-oxygen ratio. For HAT-P-26b, our observations are in good agreement with the low atmospheric metallicity inferred from transmission spectroscopy. We find that all four of the planets with detected eclipses are best matched by models with relatively efficient circulation of energy to the nightside. We see no evidence for a solar-system-like correlation between planet mass and atmospheric metallicity, but instead identify a potential (1.9 sigma) correlation between the inferred methane/(carbon monoxide + carbon dioxide) ratio and stellar metallicity. Our ability to characterize this potential trend is limited by the relatively large uncertainties in the stellar metallicity values. Our observations provide a first look at the brightness of these planets at wavelengths accessible to the James Webb Space Telescope, which will be able to resolve individual methane, carbon monoxide, and carbon dioxide bands and provide much stronger constraints on their atmospheric compositions.

arXiv comment24 pages, 25 figures, accepted for publication in AJ

References in corpus (88)

• emcee: The MCMC Hammer
• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• Analytic Lightcurves for Planetary Transit Searches
• batman: BAsic Transit Model cAlculatioN in Python
• The effects of snowlines on C/O in planetary atmospheres
• A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
• A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres
• Theoretical Transmission Spectra During Extrasolar Giant Planet Transits
• Detection of Thermal Emission from an Extrasolar Planet
• Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope
• Homogeneous studies of transiting extrasolar planets. IV. Thirty systems with space-based light curves
• Abundances of the elements in the solar system
• Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
• Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets
• The 3.6-8.0 Micron Broadband Emission Spectrum of HD 209458b: Evidence for an Atmospheric Temperature Inversion
• Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
• The Mass-Metallicity Relation for Giant Planets
• Metallicity and Temperature Indicators in M dwarf K band Spectra: Testing New & Updated Calibrations With Observations of 133 Solar Neighborhood M dwarfs
• Gaseous Mean Opacities for Giant Planet and Ultracool Dwarf Atmospheres over a Range of Metallicities and Temperatures
• The GAPS Programme with HARPS-N@TNG XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets
• Friends of Hot Jupiters I: A Radial Velocity Search for Massive, Long-Period Companions to Close-In Gas Giant Planets
• A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b
• Improved spectroscopic parameters for transiting planet hosts
• Transitions in the cloud composition of hot Jupiters
• SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs I. New atmospheric parameters and masses for 48 stars with planets
• Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b
• The Effect of Condensates on the Characterization of Transiting Planet Atmospheres with Transmission Spectroscopy
• Compositional diversity in the atmospheres of hot Neptunes, with application to GJ 436b
• Inference of Inhomogeneous Clouds in an Exoplanet Atmosphere
• Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-Level Decorrelation
• Water Vapour Absorption in the Clear Atmosphere of an exo-Neptune
• An ultrahot gas-giant exoplanet with a stratosphere
• Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars III. Iron, Magnesium, and Silicon
• The Heavy Element Masses of Extrasolar Giant Planets, Revealed
• Thermal Emission and Albedo Spectra of Super Earths with Flat Transmission Spectra
• A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
• Quantitatively Assessing the Role of Clouds in the Transmission Spectrum of GJ 1214b
• Dynamic Meteorology at the Photosphere of HD 209458b
• HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance
• On the Anomalous Radii of the Transiting Extrasolar Planets
• Bayesian Analysis of Hot Jupiter Radius Anomalies: Evidence for Ohmic Dissipation?
• A consistent retrieval analysis of 10 Hot Jupiters observed in transmission
• Detection of titanium oxide in the atmosphere of a hot Jupiter
• High-Resolution Spectroscopic Detection of TiO and Stratosphere in the Day-side of WASP-33b
• Dynamic mineral clouds on HD 189733b I. 3D RHD with kinetic, non-equilibrium cloud formation
• Evidence of an Upper Bound on the Masses of Planets and its Implications for Giant Planet Formation
• HAT-P-20b--HAT-P-23b: Four Massive Transiting Extrasolar Planets
• Pseudo 2D chemical model of hot Jupiter atmospheres: application to HD 209458b and HD 189733b
• Balancing the Energy Budget of Short-Period Giant Planets: Evidence for Reflective Clouds and Optical Absorbers
• HAT-P-12b: A Low-Density Sub-Saturn Mass Planet Transiting a Metal-Poor K Dwarf
• Forward and Inverse Modeling of the Emission and Transmission Spectrum of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds
• Three sub-Jupiter-mass planets: WASP-69b & WASP-84b transit active K dwarfs and WASP-70Ab transits the evolved primary of a G4+K3 binary
• HAT-P-26b: A Low-Density Neptune-Mass Planet Transiting a K Star
• A global analysis of Spitzer and new HARPS data confirms the loneliness and metal-richness of GJ 436 b
• Connecting Giant Planet Atmosphere and Interior Modeling: Constraints on Atmospheric Metal Enrichment
• WASP-80b has a dayside within the T-dwarf range
• Detection of sodium in the atmosphere of WASP-69b
• A Sensitive Search for Variability in Late L Dwarfs: The Quest for Weather
• Metal enrichment leads to low atmospheric C/O ratios in transiting giant exoplanets
• Simulating the cloudy atmospheres of HD 209458 b and HD 189733 b with the 3D Met Office Unified Model
• New and updated stellar parameters for 71 evolved planet hosts. On the metallicity - giant planet connection
• HAT-P-18b and HAT-P-19b: Two Low-Density Saturn-Mass Planets Transiting Metal-Rich K Stars
• An H-band Spectroscopic Metallicity Calibration for M Dwarfs
• Evidence for a Dayside Thermal Inversion and High Metallicity for the Hot Jupiter WASP-18b
• SWEET-Cat updated. New homogenous spectroscopic parameters
• Three-Dimensional Circulation Driving Chemical Disequilibrium in WASP-43b
• WASP-8b: Characterization of a Cool and Eccentric Exoplanet with Spitzer
• Water vapor in the spectrum of the extrasolar planet HD 189733b: 2. The eclipse
• A Search for Water in the Atmosphere of HAT-P-26b Using LDSS-3C
• Rayleigh scattering in the transmission spectrum of HAT-P-18b
• HAT-P-17b,c: A Transiting, Eccentric, Hot Saturn and a Long-period, Cold Jupiter
• Refined stellar, orbital and planetary parameters of the eccentric HAT-P-2 planetary system
• Warm Ice Giant GJ 3470b. II Revised Planetary and Stellar Parameters from Optical to Near-infrared Transit Photometry
• The Effect of 3D Transport-Induced Disequilibrium Carbon Chemistry on the Atmospheric Structure and Phase Curves and Emission Spectra of Hot Jupiter HD 189733b
• A Near-Infrared Spectroscopic Survey of 886 Nearby M Dwarfs
• The effect of metallicity on the atmospheres of exoplanets with fully coupled 3D hydrodynamics, equilibrium chemistry, and radiative transfer
• Updated Spitzer Emission Spectroscopy of Bright Transiting Hot Jupiter HD189733b
• On the Composition of Young, Directly Imaged Giant Planets
• Spitzer Secondary Eclipse Observations of Five Cool Gas Giant Planets and Empirical Trends in Cool Planet Emission Spectra
• HAT-P-15b: A 10.9-day Extrasolar Planet Transiting a Solar-type Star
• From cold to hot irradiated gaseous exoplanets: Toward an observation-based classification scheme
• Metallicity determination of M dwarfs - Expanded parameter range in metallicity and effective temperature
• Physical properties of the WASP-67 planetary system from multi-colour photometry
• The Stellar Obliquity and the Long-period planet in the HAT-P-17 Exoplanetary System
• Changes in the metallicity of gas giant planets due to pebble accretion
• Ground-based transit observations of the HAT-P-18, HAT-P-19, HAT-P-27/WASP-40 and WASP-21 systems
• Convective dynamics and disequilibrium chemistry in the atmospheres of giant planets and brown dwarfs
• Knot a Bad Idea: Testing BLISS Mapping for Spitzer Space Telescope Photometry

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