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arXiv · 1902.00001

Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) - II. A broadened sodium feature on the ultra-hot giant WASP-76b

J. V. Seidel·D. Ehrenreich·A. Wyttenbach·R. Allart·M. Lendl·L. Pino·V. Bourrier·H. M. Cegla·C. Lovis·D. Barrado·D. Bayliss·N. Astudillo-Defru·A. Deline·C. Fisher·K. Heng·R. Joseph·B. Lavie·C. Melo·F. Pepe·D. Ségrasan·S. Udry
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Abstract

High-resolution optical spectroscopy is a powerful tool to characterise exoplanetary atmospheres from the ground. The sodium D lines, with their large cross sections, are especially suited to study the upper layers of atmospheres in this context. We report on the results from HEARTS, a spectroscopic survey of exoplanet atmospheres, performing a comparative study of hot gas giants to determine the effects of stellar irradiation. In this second installation of the series, we highlight the detection of neutral sodium on the ultra-hot giant WASP-76b. We observed three transits of the planet using the HARPS high-resolution spectrograph at the ESO 3.6m telescope and collected 175 spectra of WASP-76. We repeatedly detect the absorption signature of neutral sodium in the planet atmosphere ($0.371\pm0.034\%$; $10.75 \sigma$ in a $0.75$ \r{A} passband). The sodium lines have a Gaussian profile with full width at half maximum (FWHM) of $27.6\pm2.8$ km s$^{-1}$. This is significantly broader than the line spread function of HARPS ($2.7$ km s$^{-1}$). We surmise that the observed broadening could trace the super-rotation in the upper atmosphere of this ultra-hot gas giant.

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J. V. Seidel, D. Ehrenreich, A. Wyttenbach, R. Allart, M. Lendl, L. Pino, V. Bourrier, H. M. Cegla, C. Lovis, D. Barrado, D. Bayliss, N. Astudillo-Defru, A. Deline, C. Fisher, K. Heng, R. Joseph, B. Lavie, C. Melo, F. Pepe, D. Ségrasan, S. Udry. 2019-01-30. Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) - II. A broadened sodium feature on the ultra-hot giant WASP-76b. https://doi.org/10.1051/0004-6361%2F201834776

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