Issue |
A&A
Volume 695, March 2025
|
|
---|---|---|
Article Number | A107 | |
Number of page(s) | 14 | |
Section | Planets, planetary systems, and small bodies | |
DOI | https://doi.org/10.1051/0004-6361/202452733 | |
Published online | 18 March 2025 |
The GAPS Programme at TNG
LXVII. Detection of water and preliminary characterisation of the atmospheres of the two hot Jupiters: KELT-8 b and KELT-23 Ab★
1
Department of Physics, University of Rome “Tor Vergata”,
Via della Ricerca Scientifica 1,
00133
Roma, Italy
2
INAF – Osservatorio Astrofisico di Torino,
Via Osservatorio 20,
10025
Pino Torinese, Italy
3
Department of Physics, University of Turin,
Via Pietro Giuria 1,
10125
Torino, Italy
4
Istituto di Astrofisica e Planetologia Spaziali INAF-IAPS,
Via Fosso del Cavaliere 100,
00133
Roma, Italy
5
ESO – European Southern Observatory, Alonso de Cordova,
3107
Vitacura, Santiago, Chile
6
INAF – Osservatorio Astronomico di Roma,
Via Frascati 33,
00078
Monte Porzio Catone, Italy
7
Max Planck Institute for Astronomy,
Königstuhl 17,
69117
Heidelberg, Germany
8
Fundación Galileo Galilei – INAF,
Rambla José Ana Fernandez Pérez 7,
38712
Breña Baja (La Palma), Canary Islands, Spain
9
Instituto de Astrofísica de Canarias,
C/Vía Láctea s/n,
38205
La Laguna (Tenerife), Canary Islands, Spain
10
Departamento de Astrofísica, Univ. de La Laguna,
Av. del Astrofísico Francisco Sánchez s/n,
38205
La Laguna (Tenerife), Canary Islands, Spain
11
INAF – Osservatorio Astronomico di Brera,
Via E. Bianchi 46,
23807
Merate, Italy
12
INAF – Osservatorio Astronomico di Palermo,
Piazza del Parlamento 1,
90134
Palermo, Italy
13
Department of Physics and Chemistry, University of Palermo,
Piazza Marina 61,
90133
Palermo, Italy
14
INAF – Osservatorio Astrofisico di Catania,
Via S. Sofia 78,
95123
Catania, Italy
15
Department of Physics and Astronomy Galileo Galilei, University of Padua,
Vicolo dell’Osservatorio 3,
35122
Padova, Italy
16
INAF – Osservatorio Astronomico di Padova,
Vicolo dell’Osservatorio 5,
35122
Padova, Italy
17
INAF – Osservatorio Astrofisico di Arcetri,
Largo Enrico Fermi 5,
50125
Firenze, Italy
★★ Corresponding author; mario.basilicata@inaf.it
Received:
24
October
2024
Accepted:
6
February
2025
Context. Hot Jupiters are among the most suitable targets for atmospheric studies. Expanding the number of hot gaseous giant planets with atmospheric characterisations can improve our understanding of the chemical-physical properties of their atmospheres, as well as the formation and evolution of these extreme planets.
Aims. In this work, we use high-resolution spectroscopy in the near-infrared (NIR) to search for chemical signatures in the atmospheres of the two hot Jupiters KELT-8 b (Teq = 1675−55+61 K) and KELT-23 Ab (Teq = 1561 ± 20 K) and present a first characterisation of their atmospheric properties.
Methods. We measured the transmission spectrum of each target with the near-infrared (NIR) high-resolution spectrograph GIANO-B at the TNG. We searched for atmospheric signals by cross-correlating the data with synthetic transmission spectra. To characterise the chemical-physical properties of the atmospheres of both planets, we ran two different atmospheric retrievals for each dataset: a retrieval assuming chemical equilibrium and a ‘free-chemistry’ retrieval, in which the abundance of each molecule could vary freely.
Results. We detect water vapour (H2O) in the atmospheres of both KELT-8 b and KELT-23 Ab with a signal-to-noise ratio of S/N = 6.6 and S/N = 4.2, respectively. The two retrievals indicate a water-rich atmosphere for both targets. In the case of KELT-8 b, we determine a water volume mixing ratio of log10 (VMRH2O) = −2.07−0.72+0.53, a metallicity of [M/H = 0.77−0.89+0.61 dex, and a sub-solar C/O ratio (C/O ≤0.30, at 2 σ). For KELT-23 Ab, we find log10 (VMRH2O) = −2.26−1.24+0.75, [M/H]= −0.42−1.35+1.56 dex, and C/O ratio ≤0.78 (at 2 σ). The constraints on the metallicity and C/O ratio are based on the assumption of chemical equilibrium. Comparing these atmospheric chemical properties with those of the host stars, we suggest that for both planets, the accretion of gaseous material occurred within the H2O snowline in a pebble-rich disk enriched in oxygen due to sublimation of water ice from the inward-drifting pebbles.
Conclusions. We investigated the atmospheres of KELT-8 b and KELT-23 Ab for the first time, finding water vapour in both of them and placing first constraints on their properties. These two planets are promising targets for future high- and low-resolution observations.
Key words: techniques: spectroscopic / planets and satellites: atmospheres / planets and satellites: individual: KELT-8 b / planets and satellites: individual: KELT-23 Ab
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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