Bibcode
Eschen, Yoshi Nike Emilia; Wilson, Thomas G.; Collier Cameron, Andrew; Mustill, Alexander James; Egger, Jo Ann; Ulmer-Moll, Solène; Gandolfi, Davide; Smith, Alexis M. S.; Demangeon, Olivier D. S.; Sousa, Sérgio G.; Bonfanti, Andrea; Correia, Alexandre C. M.; Adibekyan, Vardan; Lacedelli, Gaia; Brandeker, Alexis; Pezzotti, Camilla; Akinsanmi, Babatunde; Alibert, Yann; Alonso, Roi; Bárczy, Tamas; Barrado, David; Barros, Susana C. C.; Baumjohann, Wolfgang; Benz, Willy; Billot, Nicolas; Borsato, Luca; Broeg, Christopher; Castro-González, Amadeo; Csizmadia, Szilard; Cubillos, Patricio E.; Davies, Melvyn B.; Deleuil, Magali; Deline, Adrien; Demory, Brice-Olivier; Derekas, Aliz; Di Persio, Giuseppe; Edwards, Billy; Ehrenreich, David; Erikson, Anders; Fortier, Andrea; Fossati, Luca; Fridlund, Malcolm; Gazeas, Kosmas; Gillon, Michaël; Güdel, Manuel; Günther, Maximilian N.; Heitzmann, Alexis; Helling, Ch; Isaak, Kate G.; Jenkins, Jon M.; Keller, Tatiana; Kiss, Laszlo L.; Kitzmann, Daniel; Korth, Judith; Lam, Kristine W. F.; Laskar, Jacques; Lecavelier des Etangs, Alain; Leleu, Adrien; Lendl, Monika; Magrin, Demetrio; Maxted, Pierre F. L.; Merín, Bruno; Mordasini, Christoph; Nascimbeni, Valerio; Olofsson, Göran; Osborn, Hugh P.; Ottensamer, Roland; Pagano, Isabella; Pallé, Enric; Peter, Gisbert; Petitpas, Glen; Piazza, Daniele; Piotto, Giampaolo; Pollacco, Don; Queloz, Didier; Ragazzoni, Roberto; Rando, Nicola; Rauer, Heike; Ribas, Ignasi; Santos, Nuno C.; Scandariato, Gaetano; Ségransan, Damien; Shporer, Avi; Silva, André M.; Simon, Attila E.; Southworth, Richard; Stalport, Manu; Sulis, Sophia; Szabó, Gyula M.; Udry, Stéphane; Ulmer, Bernd; Van Grootel, Valérie; Venturini, Julia; Villaver, Eva; Walton, Nicholas A.; Wolf, Sebastian; Ziegler, Carl; Zingales, Tiziano
Bibliographical reference
Monthly Notices of the Royal Astronomical Society
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7
2026
Citations
0
Refereed citations
0
Description
We report the discovery and characterization of the multiplanetary system around TOI-4311, a K dwarf kinematically between the Galactic thick disc and Hercules stream. TOI-4311 hosts an ultra-short-period super-Earth (P$\sim$0.99 d, $1.376^{+0.077}_{-0.080}$ R$_{\oplus }$) and a longer period sub-Neptune (P$\sim$15 d, $2.47^{+0.12}_{-0.11}$ R$_{\oplus }$) that was first detected in the Transiting Exoplanet Survey Satellite photometry. Using follow-up observations with CHaracterising ExOPlanet Satellite and High Accuracy Radial Velocity Planet Searcher (HARPS), we refine the planetary radius of both planets, derive the mass of planet b ($4.5^{+1.5}_{-1.4}$ M$_{\oplus }$), and confirm the planetary nature of planet c. Intriguingly, a third periodic signal is clearly detected in our HARPS Radial Velocities (RVs) that we cannot link to stellar activity. This signal could be attributed to a third planet (P$\sim$38 d, Msin(i) = $26.4^{+6.3}_{-6.8}$ M$_{\oplus }$) in the system; however, with the current photometric data set we do not find a transit. Our dynamical analysis highlights that this potential outer planet would remain stable. Using the precise radius and mass for TOI-4311 b, we model its interior structure and find that it is very dense given the host star's galactic kinematics and chemistry. Hence, this system could challenge current formation theories and provide insights into planet formation across the galaxy.