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Carone, L.; Molliere, P.; Zhou, YF.; Bouwman, J.; Yan, F.; Baeyens, R.; Apai, D.; Espinoza, N.; Rackham, BV.; Jordan, A.; Angerhausen, D.; Decin, L.; Lendl, M.; Venot, O.; Henning, T. |
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Title |
Indications for very high metallicity and absence of methane in the eccentric exo-Saturn WASP-117b |
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2021 |
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Astronomy & Astrophysics |
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Astron. Astrophys. |
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646 |
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A168 |
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methods: observational; planets and satellites: atmospheres |
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Aims. We investigate the atmospheric composition of the long-period (P-orb = 10 days) eccentric exo-Saturn WASP-117b. WASP-117b could be similar in atmospheric temperature and chemistry to WASP-107b. In mass and radius, WASP-117b is similar to WASP-39b, which allows a comparative study of these planets.Methods. We analyzed a near-infrared transmission spectrum of WASP-117b taken with the Hubble Space Telescope (HST) WFC3 G141, which was reduced with two independent pipelines. High-resolution measurements were taken with VLT/ESPRESSO in the optical.Results. We report the robust (3 sigma) detection of a water spectral feature. In a 1D atmosphere model with isothermal temperature, uniform cloud deck, and equilibrium chemistry, the Bayesian evidence of a retrieval analysis of the transmission spectrum indicates a preference for a high atmospheric metallicity
[Fe/H] = 2.58(-0.37)(+0.26)
[Fe/H]=2.58-0.37+0.26 and clear skies. The data are also consistent with a lower metallicity composition [Fe/H] < 1.75 and a cloud deck between 10(-2.2) and 10(-5.1) bar, but with weaker Bayesian preference. We retrieve a low CH4 abundance of <10(-4) volume fraction within 1 sigma and <2 x 10(-1) volume fraction within 3<sigma>. We cannot constrain the equilibrium temperature between theoretically imposed limits of 700 and 1000 K. Further observations are needed to confirm quenching of CH4 with K-zz >= 10(8) cm(2) s(-1). We report indications of Na and K in the VLT/ESPRESSO high-resolution spectrum with substantial Bayesian evidence in combination with HST data. |
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0004-6361 |
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WOS:000624484900001 |
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UAI @ alexi.delcanto @ |
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1353 |
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