arXiv · 2510.12783
An Ultra-Short Period Super-Earth and Sub-Neptune Spanning the Radius Valley Orbiting the Kinematic Thick Disk Star TOI-2345
Abstract
A crucial chemical link between stars and their orbiting exoplanets is thought to exist. If universal, this connection could affect the formation and evolution of all planets. Therefore, this potential vital link needs testing by characterising exoplanets around chemically-diverse stars. We present the discovery of two planets orbiting the metal-poor, kinematic thick-disk K-dwarf TOI-2345. TOI-2345 b is a super-Earth with a period of 1.05 days and TOI-2345 c is a sub-Neptune with a period of 21 days. In addition to the target being observed in 4 TESS sectors, we obtained 5 CHEOPS visits and 26 radial velocities from HARPS. By conducting a joint analysis of all the data, we find TOI-2345 b to have a radius of $1.504\substack{+0.047\\-0.044}$ R$_\oplus$ and a mass of $3.49\pm0.85$ M$_\oplus$; and TOI-2345 c to have a radius of $2.451\substack{+0.045\\-0.046}$ R$_\oplus$ and a mass of $7.27\substack{+2.27\\-2.45}$ M$_\oplus$. To explore chemical links between these planets and their host star, we model their interior structures newly accounting for devolatised stellar abundances. TOI-2345 adds to the limited sample of well characterised planetary systems around thick disk stars. This system challenges theories of formation and populations of planets around thick disk stars with its Ultra-Short Period super-Earth and the wide period distribution of these two planets spanning the radius valley.
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Yoshi Nike Emilia Eschen, Thomas G. Wilson, Andrea Bonfanti, Carina M. Persson, Sérgio G. Sousa, Monika Lendl, Alexis Heitzmann, Attila E. Simon, Göran Olofsson, Amadeo Castro-González, Jo Ann Egger, Luca Fossati, Alexander James Mustill, Hugh P. Osborn, Hugo G. Vivien, Yann Alibert, Roi Alonso, Tamas Bárczy, David Barrado, Susana C. C. Barros, Wolfgang Baumjohann, Willy Benz, Nicolas Billot, Luca Borsato, Alexis Brandeker, Christopher Broeg, Maximilian Buder, Douglas A. Caldwell, Andrew Collier Cameron, Alexandre C. M. Correia, Szilard Csizmadia, Patricio E. Cubillos, Melvyn B. Davies, Magali Deleuil, Adrien Deline, Olivier D. S. Demangeon, Brice-Olivier Demory, Aliz Derekas, Billy Edwards, David Ehrenreich, Anders Erikson, Jacopo Farinato, Andrea Fortier, Malcolm Fridlund, Davide Gandolfi, Kosmas Gazeas, Michaël Gillon, Robert Goeke, Manuel Güdel, Maximilian N. Günther, Johann Hasiba, Ch. Helling, Kate G. Isaak, Jon M. Jenkins, Tatiana Keller, Laszlo L. Kiss, Daniel Kitzmann, Judith Korth, Kristine W. F. Lam, Jacques Laskar, Alain Lecavelier des Etangs, Adrien Leleu, Demetrio Magrin, Pierre F. L. Maxted, Bruno Merín, Christoph Mordasini, Valerio Nascimbeni, Roland Ottensamer, Isabella Pagano, Enric Pallé, Gisbert Peter, Daniele Piazza, Giampaolo Piotto, Don Pollacco, Didier Queloz, Roberto Ragazzoni, Nicola Rando, Francesco Ratti, Heike Rauer, Ignasi Ribas, Nuno C. Santos, Gaetano Scandariato, Damien Ségransan, Avi Shporer, Alexis M. S. Smith, Manu Stalport, Sophia Sulis, Gyula M. Szabó, Stéphane Udry, Solène Ulmer-Moll, Valérie Van Grootel, Julia Venturini, Eva Villaver, Nicholas A. Walton, David Watanabe, Sebastian Wolf, Carl Ziegler. 2025-10-14. An Ultra-Short Period Super-Earth and Sub-Neptune Spanning the Radius Valley Orbiting the Kinematic Thick Disk Star TOI-2345. https://arxiv.org/abs/2510.12783
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