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 - 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 -