Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS): VII. Detection of sodium on the long-transiting inflated sub-Saturn KELT-11 b
AffiliationDepartment of Astronomy and Steward Observatory, University of Arizona,
Planets and satellites: atmospheres
Planets and satellites: individual: KELT-11 b
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CitationMounzer, D., Lovis, C., Seidel, J. V., Attia, O., Allart, R., Bourrier, V., ... & Sousa, S. (2022). Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS)-VII. Detection of sodium on the long-transiting inflated sub-Saturn KELT-11 b. Astronomy & Astrophysics, 668, A1.
JournalAstronomy and Astrophysics
Rights© D. Mounzer et al. 2022. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractContext. High-resolution transmission spectroscopy has allowed for in-depth information on the composition and structure of exoplanetary atmospheres to be garnered in the last few years, especially in the visible and in the near-infrared. Many atomic and molecular species have been detected thanks to data gathered from state-of-the-art spectrographs installed on large ground-based telescopes. Nevertheless, the Earth daily cycle has been limiting observations to exoplanets with the shortest transits. Aims. The inflated sub-Saturn KELT-11 b has a hot atmosphere and orbits a bright evolved subgiant star, making it a prime choice for atmospheric characterization. The challenge lies in its transit duration - of more than 7 h - which can only be covered partially or without enough out-of-transit baselines when observed from the ground. Methods. To overcome this constraint, we observed KELT-11 b with the HARPS spectrograph in series of three consecutive nights, each focusing on a different phase of the planetary orbit: before, during, and after the transit. This allowed us to gather plenty of out-of-transit baseline spectra, which was critical to build a spectrum of the unocculted star with sufficient precision. Telluric absorption lines were corrected using the atmospheric transmission code MOLECFIT. Individual high-resolution transmission spectra were merged to obtain a high signal-to-noise transmission spectrum to search for sodium in KELT-11 b's atmosphere through the ~5900 Å doublet. Results. Our results highlight the potential for independent observations of a long-transiting planet over consecutive nights. Our study reveals a sodium excess absorption of 0.28 ± 0.05% and 0.50 ± 0.06% in the Na D1 and D2 lines, respectively. This corresponds to 1.44 and 1.69 times the white-light planet radius in the line cores. Wind pattern modeling tends to prefer day-to-night side winds with no vertical winds, which is surprising considering the planet bloatedness. The modeling of the Rossiter-Mclaughlin effect yields a significantly misaligned orbit, with a projected spin-orbit angle of λ = 77.86 2.26+2.36a. Conclusions. Belonging to the under-studied group of inflated sub-Saturns, the characteristics of KELT-11 b - notably its extreme scale height and long transit - make it an ideal and unique target for next-generation telescopes. Our results as well as recent findings from HST, TESS, and CHEOPS observations could make KELT-11 b a benchmark exoplanet in atmospheric characterization. © D. Mounzer et al. 2022.
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Except where otherwise noted, this item's license is described as © D. Mounzer et al. 2022. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License.