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Characterizing Exoplanetary Atmospheres at High Resolution with SPIRou: Detection of Water on HD 189733 b

A. Boucher, A. Darveau-Bernier, S. Pelletier, D. Lafrenière, E. Artigau, N. J. Cook, R. Allart, M. Radica, R. Doyon, B. Benneke, L. Arnold, X. Bonfils, V. Bourrier, R. Cloutier, J. Gomes da Silva, E. Deibert, X. Delfosse, J.-F. Donati, D. Ehrenreich, P. Figueira, T. Forveille, P. Fouqué, J. Gagné, E. Gaidos, G. Hébrard, R. Jayawardhana, B. Klein, C. Lovis, J. H. C. Martins, E. Martioli, C. Moutou, N. C. Santos

We present the first exoplanet atmospheric detection made as part of the SPIRou Legacy Survey, a Large Observing Program of 300 nights exploiting the capabilities of SPIRou, the new near-infrared high-resolution (R ∼ 70,000) spectropolarimeter installed on the Canada–France–Hawaii Telescope (3.6 m). We observed two transits of HD 189733b, an extensively studied hot Jupiter that is known to show prominent water vapor absorption in its transmission spectrum. When combining the two transits, we successfully detect the planet's water vapor absorption at 5.9σ using a cross-correlation t-test, or with a ΔBIC > 10 using a log-likelihood calculation. Using a Bayesian retrieval framework assuming parameterized temperature–pressure (T-P) profile atmospheric models, we constrain the planet atmospheric parameters, in the region probed by our transmission spectrum, to the following values: log10 VMR[H2O] = -4.4-0.4+0.4, and Pcloud ≳ 0.2 bar (gray clouds), both of which are consistent with previous studies of this planet. Our retrieved water volume-mixing ratio is slightly subsolar; although, combining it with the previously retrieved super-solar CO abundances from other studies would imply a super-solar C/O ratio. We furthermore measure a net blueshift of the planet signal of -4.62-0.44+0.46 km s−1, which is somewhat larger than many previous measurements and unlikely to result solely from winds in the planet's atmosphere, although it could possibly be explained by a transit signal dominated by the trailing limb of the planet. This large blueshift is observed in all of the different detection/retrieval methods that were performed and in each of the two transits independently.

Exoplanet atmospheres; Exoplanet atmospheric composition; Exoplanet astronomy; Atmospheric circulation; Hot Jupiters; Molecular spectroscopy; Astronomy data analysis; Atmospheric clouds; Atmospheric composition; Transmission spectroscopy; High resolution

The Astrophysical Journal
Volume 162, Number 6
2021 December

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia