The KELT-7b atmospheric thermal-inversion conundrum revisited with CHEOPS, TESS, and additional data
Artikel i vetenskaplig tidskrift, 2025
Context. Early theoretical works suggested that ultrahot Jupiters have inverted temperature-pressure (T-P) profiles in the presence of optical absorbers, such as TiO and VO. Recently, an inverted T-P profile of KELT-7b was detected, in agreement with the predictions. However, the diagnosis of T-P inversions has always been recognized to be a model-dependent process.
Aims. We used the Characterising Exoplanet Satellite (CHEOPS), the Transiting Exoplanet Survey Satellite (TESS), and additional literature data to characterize the atmosphere of KELT-7b, rederive the T-P profile, provide a precise measurement of the albedo of KELT-7b, and search for a possible distortion in the precise CHEOPS transit light curve of the planet.
Methods. We first jointly fitted the CHEOPS and TESS data and measured the occultation depths in these passbands. The CHEOPS transits were also fitted with a model including the gravity-darkening effect. Emission and absorption retrievals were performed to characterize the atmosphere of KELT-7b. The albedo of the planet was calculated in the CHEOPS and TESS passbands.
Results. When adopting a thermochemical-equilibrium atmospheric composition, the emission retrievals return a non-inverted T-P profile, in contrast with previous results. When adopting a free-chemistry atmospheric parameterization, the emission retrievals return an inverted T-P profile with - likely unphysically - high concentrations of TiO and VO. The 3D general circulation model (GCM) supports a TiO-induced temperature inversion. We report for KELT-7b a very low geometric albedo of A(g) = 0.05 +/- 0.06, which is consistent with the heat distribution & varepsilon; being close to zero and also consistent with a 3D GCM simulation, using magnetic drag (tau(drag) = 10(4) s). Based on the CHEOPS photometry, we are unable to place any meaningful constraint on the sky-projected orbital obliquity.
Conclusions. The choice of a free-chemistry approach or a thermochemical-equilibrium chemistry is the main factor determining the retrieval results. Free-chemistry retrievals generally yield better fits; however, assuming free chemistry risks adopting unphysical scenarios for ultrahot Jupiters, such as KELT-7b. We applied a coherent stellar variability treatment on TESS and CHEOPS observations, commensurate with the known stellar activity of the host star. Other observations of KELT-7b would also benefit from a coherent stellar variability treatment.
Aims. We used the Characterising Exoplanet Satellite (CHEOPS), the Transiting Exoplanet Survey Satellite (TESS), and additional literature data to characterize the atmosphere of KELT-7b, rederive the T-P profile, provide a precise measurement of the albedo of KELT-7b, and search for a possible distortion in the precise CHEOPS transit light curve of the planet.
Methods. We first jointly fitted the CHEOPS and TESS data and measured the occultation depths in these passbands. The CHEOPS transits were also fitted with a model including the gravity-darkening effect. Emission and absorption retrievals were performed to characterize the atmosphere of KELT-7b. The albedo of the planet was calculated in the CHEOPS and TESS passbands.
Results. When adopting a thermochemical-equilibrium atmospheric composition, the emission retrievals return a non-inverted T-P profile, in contrast with previous results. When adopting a free-chemistry atmospheric parameterization, the emission retrievals return an inverted T-P profile with - likely unphysically - high concentrations of TiO and VO. The 3D general circulation model (GCM) supports a TiO-induced temperature inversion. We report for KELT-7b a very low geometric albedo of A(g) = 0.05 +/- 0.06, which is consistent with the heat distribution & varepsilon; being close to zero and also consistent with a 3D GCM simulation, using magnetic drag (tau(drag) = 10(4) s). Based on the CHEOPS photometry, we are unable to place any meaningful constraint on the sky-projected orbital obliquity.
Conclusions. The choice of a free-chemistry approach or a thermochemical-equilibrium chemistry is the main factor determining the retrieval results. Free-chemistry retrievals generally yield better fits; however, assuming free chemistry risks adopting unphysical scenarios for ultrahot Jupiters, such as KELT-7b. We applied a coherent stellar variability treatment on TESS and CHEOPS observations, commensurate with the known stellar activity of the host star. Other observations of KELT-7b would also benefit from a coherent stellar variability treatment.
planets and satellites: atmospheres
planets and satellites: fundamental parameters
techniques: photometric
methods: observational
planets and satellites: individual
Författare
Z. Garai
Eötvös Loránd University (ELTE)
Slovak Academy of Sciences
A. Krenn
Österreichische Akademie der Wissenschaften
P. E. Cubillos
Istituto nazionale di astrofisica (INAF)
Österreichische Akademie der Wissenschaften
G. Bruno
Istituto nazionale di astrofisica (INAF)
A. M. S. Smith
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
T. G. Wilson
The University of Warwick
A. Brandeker
Stockholms universitet
M. N. Guenther
Europeiska rymdorganisationen (ESA)
A. Heitzmann
Université de Genève
L. Carone
Österreichische Akademie der Wissenschaften
V. Singh
Istituto nazionale di astrofisica (INAF)
M. Lendl
Université de Genève
O. D. S. Demangeon
Universidade do Porto
Y. Alibert
Universität Bern
R. Alonso
Universidad de la Laguna
Instituto de Astrofísica de Canarias
J. Asquier
Europeiska rymdorganisationen (ESA)
T. Barczy
Admatis
D. Barrado
Consejo Superior de Investigaciones Científicas (CSIC)
S. C. C. Barros
Universidade do Porto
W. Baumjohann
Österreichische Akademie der Wissenschaften
W. Benz
Universität Bern
N. Billot
Université de Genève
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
Universität Bern
A. Collier Cameron
University of St Andrews
A. C. M. Correia
Universidade de Coimbra
Sz. Csizmadia
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
M. B. Davies
Lunds universitet
M. Deleuil
Aix-Marseille Université
A. Deline
Université de Genève
B. -o. Demory
Universität Bern
A. Derekas
Eötvös Loránd University (ELTE)
Hungarian Research Network
B. Edwards
Netherlands Institute for Space Research (SRON)
J. A. Egger
Universität Bern
D. Ehrenreich
Université de Genève
A. Erikson
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
J. Farinato
Istituto nazionale di astrofisica (INAF)
A. Fortier
Universität Bern
L. Fossati
Österreichische Akademie der Wissenschaften
Malcolm Fridlund
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
D. Gandolfi
Universita degli Studi di Torino
K. Gazeas
National and Kapodistrian University of Athens
M. Gillon
Universite de Liège
M. Guedel
Universität Wien
Ch. Helling
Technische Universität Graz
Österreichische Akademie der Wissenschaften
K. G. Isaak
Europeiska rymdorganisationen (ESA)
F. Kerschbaum
Universität Wien
L. L. Kiss
Magyar Tudomanyos Akademia
Eötvös Loránd University (ELTE)
J. Korth
Lunds universitet
K. W. F. Lam
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
J. Laskar
Sorbonne Université
A. Lecavelier des Etangs
Université Pierre et Marie Curie (UPMC)
D. Magrin
Istituto nazionale di astrofisica (INAF)
P. F. L. Maxted
Keele University
B. Merin
Europeiska rymdorganisationen (ESA)
C. Mordasini
Universität Bern
V. Nascimbeni
Istituto nazionale di astrofisica (INAF)
G. Olofsson
Stockholms universitet
R. Ottensamer
Universität Wien
I. Pagano
Istituto nazionale di astrofisica (INAF)
E. Palle
Universidad de la Laguna
Instituto de Astrofísica de Canarias
G. Peter
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
D. Piazza
Universität Bern
G. Piotto
Università di Padova
Istituto nazionale di astrofisica (INAF)
D. Pollacco
The University of Warwick
D. Queloz
Eidgenössische Technische Hochschule Zürich (ETH)
University of Cambridge
R. Ragazzoni
Istituto nazionale di astrofisica (INAF)
Università di Padova
N. Rando
Europeiska rymdorganisationen (ESA)
H. Rauer
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
Freie Universität Berlin
I. Ribas
Inst Estudis Espacials Catalunya IEEC
Consejo Superior de Investigaciones Científicas (CSIC)
N. C. Santos
Universidade do Porto
G. Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
Université de Genève
A. E. Simon
Universität Bern
S. G. Sousa
Universidade do Porto
M. Stalport
Universite de Liège
S. Sulis
Aix-Marseille Université
Gy. M. Szabo
Eötvös Loránd University (ELTE)
S. Udry
Université de Genève
S. Ulmer-Moll
Université de Genève
Universite de Liège
Universität Bern
V. Van Grootel
Universite de Liège
J. Venturini
Université de Genève
E. Villaver
Universidad de la Laguna
Instituto de Astrofísica de Canarias
N. A. Walton
University of Cambridge
S. Wolf
Universität Bern
D. Wolter
Deutsches Zentrums für Luft- und Raumfahrt (DLR)
T. Zingales
Università di Padova
Istituto nazionale di astrofisica (INAF)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 700 A5Ämneskategorier (SSIF 2025)
Astronomi, astrofysik och kosmologi
DOI
10.1051/0004-6361/202452560