The Emission Spectrum of the Hot Jupiter WASP-79b from HST/WFC3

Trevor O. Foote*, Nikole K. Lewis, Brian M. Kilpatrick, Jayesh M. Goyal, Giovanni Bruno, Hannah R. Wakeford, Nina Robbins-Blanch, Tiffany Kataria, Ryan J. MacDonald, Mercedes López-Morales, David K. Sing, Thomas Mikal-Evans, Vincent Bourrier, Gregory Henry, Lars A. Buchhave

*Corresponding author for this work

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    Here we present a thermal emission spectrum of WASP-79b, obtained via Hubble Space Telescope Wide Field Camera 3 G141 observations as part of the PanCET program. As we did not observe the ingress or egress of WASP-79b’s secondary eclipse, we consider two scenarios: a fixed mid-eclipse time based on the expected occurrence time, and a mid-eclipse time as a free parameter. In both scenarios, we can measure thermal emission from WASP-79b from 1.1 to 1.7 μm at 2.4σ confidence consistent with a 1900 K brightness temperature for the planet. We combine our observations with Spitzer dayside photometry (3.6 and 4.5 μm) and compare these observations to a grid of atmospheric forward models that span a range of metallicities, carbon-to-oxygen ratios, and recirculation factors. Given the strength of the planetary emission and the precision of our measurements, we found a wide range of forward models to be consistent with our data. The best-match equilibrium model suggests that WASP-79b’s dayside has a solar metallicity and carbon-to-oxygen ratio, alongside a recirculation factor of 0.75. Models including significant H− opacity provide the best match to WASP-79b’s emission spectrum near 1.58 μm. However, models featuring high-temperature cloud species—formed via vigorous vertical mixing and low sedimentation efficiencies—with little day-to-night energy transport also match WASP-79b’s emission spectrum. Given the broad range of equilibrium chemistry, disequilibrium chemistry, and cloudy atmospheric models consistent with our observations of WASP-79b’s dayside emission, further observations will be necessary to constrain WASP-79b’s dayside atmospheric properties.
    Original languageEnglish
    Article number7
    JournalAstronomical Journal
    Issue number1
    Number of pages11
    Publication statusPublished - 2022


    • Exoplanet atmospheric composition
    • Exoplanet atmospheres
    • Hot Jupiters
    • Exoplanets
    • Extrasolar gaseous giant planets


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