Unveiling the internal structure and formation history of the three planets transiting HIP 29442 (TOI-469) with CHEOPS

Author(s): J. A. Egger, H. P. Osborn, D. Kubyshkina, C. Mordasini, Y. Alibert, M. N. Günther, M. Lendl, A. Brandeker, A. Heitzmann, A. Leleu, M. Damasso, A. Bonfanti, T. G. Wilson, S. G. Sousa, J. Haldemann, L. Delrez, M. J. Hooton, T. Zingales, R. Luque, R. Alonso, J. Asquier, T. Bárczy, D. Barrado Navascues, S. C.C. Barros, W. Baumjohann, W. Benz, N. Billot, L. Borsato, C. Broeg, M. Buder, A. Castro-González, A. Collier Cameron, A. C.M. Correia, D. Cortes, Sz Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, A. Deline, O. D.S. Demangeon, B. O. Demory, A. Derekas, B. Edwards, D. Ehrenreich, A. Erikson, A. Fortier, L. Fossati, M. Fridlund, D. Gandolfi, K. Gazeas, M. Gillon, M. Güdel, Ch Helling, K. G. Isaak, L. L. Kiss, J. Korth, K. W.F. Lam, J. Laskar, B. Lavie, A. Lecavelier des Etangs, C. Lovis, A. Luntzer, D. Magrin, P. F.L. Maxted, B. Merín, M. Munari, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, D. Piazza, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, J. Rodrigues, N. C. Santos, G. Scandariato, D. Ségransan, A. E. Simon, A. M.S. Smith, M. Stalport, S. Sulis, Gy M. Szabó, S. Udry, V. Van Grootel, J. Venturini, E. Villaver, N. A. Walton
Abstract: Multiplanetary systems spanning the radius valley are ideal testing grounds for exploring the different proposed explanations for the observed bimodality in the radius distribution of close-in exoplanets. One such system is HIP 29442 (TOI-469), an evolved K0V star hosting two super-Earths and one sub-Neptune. We observed HIP 29442 with CHEOPS for a total of 9.6 days, which we modelled jointly with two sectors of TESS data to derive planetary radii of 3.410 ± 0.046, 1.551 ± 0.045, and 1.538 ± 0.049 R? for planets b, c, and d, which orbit HIP 29442 with periods of 13.6, 3.5, and 6.4 days, respectively. For planet d this value deviates by more than 3s from the median value reported in the discovery paper, leading us to conclude that caution is required when using TESS photometry to determine the radii of small planets with low per-transit signal-to-noise ratios and large gaps between observations. Given the high precision of these new radii, combining them with published RVs from ESPRESSO and HIRES provides us with ideal conditions to investigate the internal structure and formation pathways of the planets in the system. We introduced the publicly available code plaNETic, a fast and robust neural network-based Bayesian internal structure modelling framework. We then applied hydrodynamic models to explore the upper atmospheric properties of these inferred structures. Finally, we identified planetary system analogues in a synthetic population generated with the Bern model for planet formation and evolution. Based on this analysis, we find that the planets likely formed on opposing sides of the water iceline from a protoplanetary disk with an intermediate solid mass. We finally report that the observed parameters of the HIP 29442 system are compatible with a scenario where the second peak in the bimodal radius distribution corresponds to sub-Neptunes with a pure H/He envelope and with a scenario with water-rich sub-Neptunes.
Organisation(s): Department of Astrophysics
External organisation(s): Universität Bern, Massachusetts Institute of Technology, Österreichische Akademie der Wissenschaften (ÖAW), Science and Operations Department - Science Division (SCI-SC), Université de Genève, Stockholm University, INAF-Osservatorio Astrofisico di Torino, University of Warwick, Universidade do Porto, Université de Liège, Katholieke Universiteit Leuven, University of Cambridge, University of Padova, Osservatorio Astronomico, University of Chicago, Institute of Astrophysics of the Canary Islands, University of La Laguna, Admatis Ltd., Centro de Astrobiología (CSIC-INTA), Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), University of St. Andrews, Universidade de Coimbra, Airbus Defence and Space, Lund University, Aix-Marseille Université, Eötvös Loránd University Budapest, SRON Netherlands Institute for Space Research , Leiden University, Chalmers University of Technology, University of Turin, National & Kapodistrian University of Athens, Technische Universität Graz, HUN-REN Hungarian Research Network, Lund Observatory, Université de recherche Paris Sciences et Lettres, Université Paris VI - Pierre-et-Marie-Curie, Keele University, European Space Astronomy Centre (ESA), INAF-Osservatorio Astrofisico di Catania, Eidgenössische Technische Hochschule Zürich, Freie Universität Berlin (FU), Spanish National Research Council (CSIC), Institute of Space Studies of Catalonia (IEEC)
Journal: Astronomy and Astrophysics
Volume: 688
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/202450472
Publication date: 08-2024
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics, 103038 Space exploration
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/a0445dca-e44e-483f-a0f4-f25c0b332892

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