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The Hubble PanCET Program: A Featureless Transmission Spectrum for WASP-29b and Evidence of Enhanced Atmospheric Metallicity on WASP-80b

Wong, Ian and Chachan, Yayaati and Knutson, Heather A. and Henry, Gregory W. and Adams, Danica and Kataria, Tiffany and Benneke, Björn and Gao, Peter and Deming, Drake and López-Morales, Mercedes and Sing, David K. and Alam, Munazza K. and Ballester, Gilda E. and Barstow, Joanna K. and Buchhave, Lars A. and dos Santos, Leonardo A. and Fu, Guangwei and García Muñoz, Antonio and MacDonald, Ryan J. and Mikal-Evans, Thomas and Sanz-Forcada, Jorge and Wakeford, Hannah R. (2022) The Hubble PanCET Program: A Featureless Transmission Spectrum for WASP-29b and Evidence of Enhanced Atmospheric Metallicity on WASP-80b. Astronomical Journal, 164 (1). Art. No. 30. ISSN 0004-6256. doi:10.3847/1538-3881/ac7234.

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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.

Item Type:Article
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URLURL TypeDescription Paper
Wong, Ian0000-0001-9665-8429
Chachan, Yayaati0000-0003-1728-8269
Knutson, Heather A.0000-0002-5375-4725
Henry, Gregory W.0000-0003-4155-8513
Adams, Danica0000-0001-9897-9680
Kataria, Tiffany0000-0003-3759-9080
Benneke, Björn0000-0001-5578-1498
Gao, Peter0000-0002-8518-9601
Deming, Drake0000-0001-5727-4094
López-Morales, Mercedes0000-0003-3204-8183
Sing, David K.0000-0001-6050-7645
Alam, Munazza K.0000-0003-4157-832X
Ballester, Gilda E.0000-0002-3891-7645
Barstow, Joanna K.0000-0003-3726-5419
Buchhave, Lars A.0000-0003-1605-5666
dos Santos, Leonardo A.0000-0002-2248-3838
Fu, Guangwei0000-0002-3263-2251
García Muñoz, Antonio0000-0003-1756-4825
MacDonald, Ryan J.0000-0003-4816-3469
Mikal-Evans, Thomas0000-0001-5442-1300
Sanz-Forcada, Jorge0000-0002-1600-7835
Wakeford, Hannah R.0000-0003-4328-3867
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 March 30; revised 2022 May 13; accepted 2022 May 21; published 2022 July 1. This work is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI) operated by AURA, Inc. This work is also based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013)/ERC grant agreement no. 336792. Support for this work was also provided by NASA/STScI through grants linked to the HST-GO-12473 and HST-GO-14767 programs. Astronomy at Tennessee State University is supported by the State of Tennessee through its Centers of Excellence Program. I.W. is supported by an appointment to the NASA Postdoctoral Program at the NASA Goddard Space Flight Center, administered by the Universities Space Research Association under contract with NASA. J.S.F. acknowledges support from the Spanish State Research Agency projects AYA2016-79425-C3-2-P and PID2019-109522GB-C51. We also thank an anonymous referee for helpful comments that improved the manuscript. Facilities: AIT - , HST/STIS - , HST/WFC3 - , Spitzer/IRAC - , XMM-Newton. - Software: batman (Kreidberg 2015), dynesty (Speagle 2020), emcee (Foreman-Mackey et al. 2013), ExoTEP (Benneke et al. 2019; Wong et al. 2020a), LDTk (Parviainen & Aigrain 2015).
Funding AgencyGrant Number
European Research Council (ERC)336792
State of Tennessee Centers of Excellence programUNSPECIFIED
NASA Postdoctoral ProgramUNSPECIFIED
Agencia Estatal de InvestigaciónAYA2016-79425-C3-2-P
Agencia Estatal de InvestigaciónPID2019-109522GB-C51
Subject Keywords:Exoplanet atmospheres; Exoplanet atmospheric composition; Transmission spectroscopy
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet atmospheres (487); Exoplanet atmospheric composition (2021); Transmission spectroscopy (2133)
Record Number:CaltechAUTHORS:20220705-671943000
Persistent URL:
Official Citation:Ian Wong et al 2022 AJ 164 30
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115314
Deposited By: George Porter
Deposited On:08 Jul 2022 21:44
Last Modified:25 Jul 2022 23:14

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