Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity

Abstract

We examine the spectra and infrared colors of the cool methane-dominated atmospheres at Teff < 1400 K expected for young gas giant planets. We couple these spectral calculations to an updated version of the Marley et al. (2007) giant planet thermal evolution models that include formation by core accretion-gas capture. These relatively cool "young Jupiters" can be 1-6 magnitudes fainter than predicted by standard cooling tracks that include a traditional initial condition, which may provide a diagnostic of formation. If correct, this would make true Jupiter-like planets much more difficult to detect at young ages than previously thought. Since Jupiter and Saturn are of distinctly super-solar composition, we examine emitted spectra for model planets at both solar metallicity and a metallicity of 5 times solar. These metal-enhanced young Jupiters have lower pressure photospheres than field brown dwarfs of the same effective temperatures arising from both lower surface gravities and enhanced atmospheric opacity. We highlight several diagnostics for enhanced metallicity. A stronger CO absorption band at 4.5 $\mu$m for the warmest objects is predicted. At all temperatures, enhanced flux in $K$ band is expected due to reduced collisional induced absorption by H${}_2$. This leads to correspondingly redder near infrared colors, which are redder than solar metallicity models with the same surface gravity by up to 0.7 in $J-K$ and 1.5 in $H-K$. Molecular absorption band depths increase as well, most significantly for the coolest objects. We also qualitatively assess the changes to emitted spectra due to nonequilibrium chemistry.

Accepted to ApJ. Most figures in color

References in corpus (12)

• On the Luminosity of Young Jupiters
• Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• The Gemini Deep Planet Survey -- GDPS
• Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
• Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
• A Systematic Study of Departures from Chemical Equilibrium in the Atmospheres of Substellar Mass Objects
• HD 203030B: an Unusually Cool Young Sub-Stellar Companion near the L/T Transition
• Physical parameters of two very cool T dwarfs
• Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI and Direct Adaptive Optics Imaging Surveys: Giant Planets are Rare at Large Separations
• Analysis of Spitzer Spectra of Irradiated Planets: Evidence for Water Vapor?
• A Survey for Massive Giant Planets in Debris Disks with Evacuated Inner Cavities

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