TY - JOUR
T1 - Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS)
T2 - VII. Detection of sodium on the long-transiting inflated sub-Saturn KELT-11 b
AU - Mounzer, D.
AU - Lovis, C.
AU - Seidel, J. V.
AU - Attia, O.
AU - Allart, R.
AU - Bourrier, V.
AU - Ehrenreich, D.
AU - Wyttenbach, A.
AU - Astudillo-Defru, N.
AU - Beatty, T. G.
AU - Cegla, H.
AU - Heng, K.
AU - Lavie, B.
AU - Lendl, M.
AU - Melo, C.
AU - Pepe, F.
AU - Pepper, J.
AU - Rodriguez, J. E.
AU - Ségransan, D.
AU - Udry, S.
AU - Linder, E.
AU - Sousa, S.
N1 - Funding Information:
We acknowledge the Geneva exoplanet atmospheres group for their helpful feedback. We thank the referee for insightful comments that helped improve the manuscript. This work has been carried out within the framework of the National Centre of Competence in Research PlanetS supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. The authors acknowledge the financial support of the SNSF. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (project F our A ces , grant agreement no. 724427; project S pice D une , grant agreement no. 947634). R.A. is a Trottier Postdoctoral Fellow and acknowledges support from the Trottier Family Foundation. This work was supported in part through a grant from FRQNT. M.L. acknowledges support of the Swiss National Science Foundation under grant number PCEFP2_194576.
Publisher Copyright:
© D. Mounzer et al. 2022.
PY - 2022/12/1
Y1 - 2022/12/1
N2 - Context. 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.
AB - Context. 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.
KW - Instrumentation: spectrographs
KW - Methods: observational
KW - Planets and satellites: atmospheres
KW - Planets and satellites: individual: KELT-11 b
KW - Techniques: spectroscopic
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U2 - 10.1051/0004-6361/202243998
DO - 10.1051/0004-6361/202243998
M3 - Article
AN - SCOPUS:85145265327
SN - 0004-6361
VL - 668
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A1
ER -