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Wong, Ian; Chachan, Yayaati; Knutson, Heather A.; Henry, Gregory W.; Adams, Danica; Kataria, Tiffany; Benneke, Björn; Gao, Peter; Deming, Drake; López-Morales, Mercedes; Sing, David K.; Alam, Munazza K.; Ballester, Gilda E.; Barstow, Joanna K.; Buchhave, Lars A.; dos Santos, Leonardo A.; Fu, Guangwei; Muñoz, Antonio García; MacDonald, Ryan J.; Mikal-Evans, Thomas; Sanz-Forcada, Jorge and Wakeford, Hannah R.
(2022).
DOI: https://doi.org/10.3847/1538-3881/ac7234
Abstract
We present a uniform analysis of transit observations from the Hubble Space Telescope and Spitzer Space Telescope of two warm gas giants orbiting K-type stars—WASP-29b and WASP-80b. The transmission spectra, which span 0.4–5.0 μm, are interpreted using a suite of chemical equilibrium PLATON atmospheric retrievals. Both planets show evidence of significant aerosol opacity along the day–night terminator. The spectrum of WASP-29b is flat throughout the visible and near-infrared, suggesting the presence of condensate clouds extending to low pressures. The lack of spectral features hinders our ability to constrain the atmospheric metallicity and C/O ratio. In contrast, WASP-80b shows a discernible, albeit muted H2O absorption feature at 1.4 μm, as well as a steep optical spectral slope that is caused by fine-particle aerosols and/or contamination from unocculted spots on the variable host star. WASP-80b joins the small number of gas-giant exoplanets that show evidence for enhanced atmospheric metallicity: the transmission spectrum is consistent with metallicities ranging from ∼30–100 times solar in the case of cloudy limbs to a few hundred times solar in the cloud-free scenario. In addition to the detection of water, we infer the presence of CO2 in the atmosphere of WASP-80b based on the enhanced transit depth in the Spitzer 4.5 μm bandpass. From a complementary analysis of Spitzer secondary eclipses, we find that the dayside emission from WASP-29b and WASP-80b is consistent with brightness temperatures of 937 ± 48 and 851 ± 14 K, respectively, indicating relatively weak day–night heat transport and low Bond albedo.