Characterisation of the TOI-421 planetary system using CHEOPS, TESS, and archival radial velocity data

Autor(en): A. F. Krenn, D. Kubyshkina, L. Fossati, J. A. Egger, A. Bonfanti, A. Deline, D. Ehrenreich, M. Beck, W. Benz, J. Cabrera, T. G. Wilson, A. Leleu, S. G. Sousa, V. Adibekyan, A. C.M. Correia, Y. Alibert, L. Delrez, M. Lendl, J. A. Patel, J. Venturini, R. Alonso, G. Anglada, J. Asquier, T. Bárczy, D. Barrado Navascues, S. C.C. Barros, W. Baumjohann, T. Beck, N. Billot, X. Bonfils, L. Borsato, A. Brandeker, C. Broeg, S. Charnoz, A. Collier Cameron, Sz Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, O. D.S. Demangeon, B. O. Demory, A. Erikson, A. Fortier, M. Fridlund, D. Gandolfi, M. Gillon, M. Güdel, M. N. Günther, J. Hasiba, A. Heitzmann, C. Helling, S. Hoyer, K. G. Isaak, L. L. Kiss, K. W.F. Lam, J. Laskar, A. Lecavelier Des Etangs, C. Lovis, D. Magrin, P. F.L. Maxted, C. Mordasini, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, M. Rieder, N. C. Santos, G. Scandariato, D. Ségransan, A. E. Simon, A. M.S. Smith, M. Stalport, M. Steller, Gy M. Szabó, N. Thomas, S. Udry, B. Ulmer, V. Van Grootel, E. Villaver, V. Viotto, N. A. Walton, T. Zingales
Abstrakt: Context. The TOI-421 planetary system contains two sub-Neptune-type planets (P_b ~ 5.2 days, T_eq_b ~ 900 K, and P_c ~ 16.1 days, T_eq,c ~ 650 K) and is a prime target to study the formation and evolution of planets and their atmospheres. The inner planet is especially interesting as the existence of a hydrogen-dominated atmosphere at its orbital separation cannot be explained by current formation models without previous orbital migration. Aims. We aim to improve the system parameters to further use them to model the interior structure and simulate the atmospheric evolution of both planets, to finally gain insights into their formation and evolution. We also investigate the possibility of detecting transit timing variations (TTVs). Methods. We jointly analysed photometric data of three TESS sectors and six CHEOPS visits as well as 156 radial velocity data points to retrieve improved planetary parameters. We also searched for TTVs and modelled the interior structure of the planets. Finally, we simulated the evolution of the primordial H-He atmospheres of the planets using two different modelling frameworks. Results. We determine the planetary radii and masses of TOI-421 b and c to be R_b = 2.64 ± 0.08 R, M_b = 6.7 ± 0.6 M, R_c = 5.09 ± 0.07 R, and M_c = 14.1 ± 1.4 M. Using these results we retrieved average planetary densities of ρ_b = 0.37 ± 0.05ρ and ρ_c = 0.107 ± 0.012 ρ. We do not detect any statistically significant TTV signals. Assuming the presence of a hydrogen-dominated atmosphere, the interior structure modelling results in both planets having extensive envelopes. While the modelling of the atmospheric evolution predicts for TOI-421 b to have lost any primordial atmosphere that it could have accreted at its current orbital position, TOI-421 c could have started out with an initial atmospheric mass fraction somewhere between 10 and 35%. Conclusions. We conclude that the low observed mean density of TOI-421 b can only be explained by either a bias in the measured planetary parameters (e.g. driven by high-altitude clouds) and/or in the context of orbital migration. We also find that the results of atmospheric evolution models are strongly dependent on the employed planetary structure model.
Organisation(en): Institut für Astrophysik
Externe Organisation(en): Österreichische Akademie der Wissenschaften (ÖAW), Universität Bern, Universität Genf, Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), University of St. Andrews, Universidade do Porto, Universidade de Coimbra, Université de Liège, Stockholm University, Instituto de Astrofísica de Canarias (IAC), Universidad de La Laguna, Spanish National Research Council (CSIC), Institut d'Estudis Espacials de Catalunya (IEEC), European Space Research & Technology Centre (ESA/ESTEC), Admatis, European Space Astronomy Centre (ESA), Université Grenoble-Alpes, INAF - Osservatorio Astronomico di Padova, Université de Paris, INAF-Osservatorio Astrofisico di Torino, Lund University, Aix-Marseille Université, Leiden University, Chalmers University of Technology, Università degli Studi di Torino, Technische Universität Graz, MTA Társadalomtudományi Kutatóközpont, Eötvös Loránd University Budapest, Université de recherche Paris Sciences et Lettres, Centre National De La Recherche Scientifique (CNRS), Keele University, INAF-Osservatorio Astrofisico di Catania, Università degli Studi di Padova, University of Warwick, Eidgenössische Technische Hochschule Zürich, University of Cambridge, Technische Universität Berlin, Freie Universität Berlin (FU)
Journal: Astronomy and Astrophysics
Band: 686
Anzahl der Seiten: 20
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/202348584
Publikationsdatum: 06-2024
Peer-reviewed: Ja
ÖFOS 2012: 103003 Astronomie, 103004 Astrophysik, 103038 Weltraumforschung
Schlagwörter
ASJC Scopus Sachgebiete: Astronomy and Astrophysics, Space and Planetary Science
Link zum Portal: https://ucrisportal.univie.ac.at/de/publications/b7131255-ef0a-4519-8352-ef4d61eb6e32

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