Uncovering the true periods of the young sub-Neptunes orbiting TOI-2076
Alonso, R.; Bouchy, F.; Deleuil, M.; Erikson, A.; Fridlund, M.; Queloz, D.; Rauer, H.; Olofsson, G.; Pallé, E.; Ribas, I.; Heng, K.; Güdel, M.; Isaak, K. G.; Scandariato, G.; Pagano, I.; Steller, M.; Thomas, N.; Baumjohann, W.; Gandolfi, D.; Fossati, L.; Smith, A. M. S.; Cabrera, J.; Ségransan, D.; Ragazzoni, R.; Piotto, G.; Serrano, L. M.; Benz, W.; Collier Cameron, A.; Alibert, Y.; Delrez, L.; Fortier, A.; Hoyer, S.; Bonfanti, A.; Salmon, S.; Sousa, S. G.; Wilson, T. G.; Bárczy, T.; Barros, S. C. C.; Beck, T.; Bonfils, X.; Borsato, L.; Brandeker, A.; Broeg, C.; Charnoz, S.; Collins, K. A.; Davies, M. B.; Demangeon, O. D. S.; Demory, B. -O.; Ehrenreich, D.; Gillon, M.; Hooton, M. J.; Laskar, J.; Lecavelier des Etangs, A.; Lendl, M.; Lovis, C.; Magrin, D.; Maxted, P. F. L.; Nascimbeni, V.; Osborn, H. P.; Ottensamer, R.; Peter, G.; Pollacco, D.; Rando, N.; Simon, A. E.; Udry, S.; Van Grootel, V.; Anglada, G.; Szabó, G. M.; Sabin, L.; Malavolta, L.; Schwarz, R. P.; Barrado y Navascues, D.; Futyan, D.; Kiss, L.; Walton, N.; McCormac, J.; Parviainen, H.; Asquier, J.; Piazza, D.; Walter, I.; Csizmadia, S.; Leleu, A.; Hedges, C.; Shporer, A.; Ulmer-Moll, S.; Gómez Maqueo Chew, Y.; Schanche, N.; Schroffenegger, U.; Wells, R. D.; Santos, N.; Biondi, F.; Tuson, A.; Reimers, C.; Gomes da Silva, J.; Gutermann, P.; Gömez-Munoz, M. A.
Switzerland, United States, Austria, Italy, France, United Kingdom, Portugal, Mexico, Spain, Belgium, Netherlands, Germany, Sweden, Hungary
Abstract
Context. TOI-2076 is a transiting three-planet system of sub-Neptunes orbiting a bright (G = 8.9 mag), young (340 ± 80 Myr) K-type star. Although a validated planetary system, the orbits of the two outer planets were unconstrained as only two non-consecutive transits were seen in TESS photometry. This left 11 and 7 possible period aliases for each.
Aims: To reveal the true orbits of these two long-period planets, precise photometry targeted on the highest-probability period aliases is required. Long-term monitoring of transits in multi-planet systems can also help constrain planetary masses through TTV measurements.
Methods: We used the MonoTools package to determine which aliases to follow, and then performed space-based and ground-based photometric follow-up of TOI-2076 c and d with CHEOPS, SAINT-EX, and LCO telescopes.
Results: CHEOPS observations revealed a clear detection for TOI-2076 c at P = 21.02538 - 0.00074 + 0.00084 d, and allowed us to rule out three of the most likely period aliases for TOI-2076 d. Ground-based photometry further enabled us to rule out remaining aliases and confirm the P = 35.12537 ± 0.00067 d alias. These observations also improved the radius precision of all three sub-Neptunes to 2.518 ± 0.036, 3.497 ± 0.043, and 3.232 ± 0.063 R⊕. Our observations also revealed a clear anti-correlated TTV signal between planets b and c likely caused by their proximity to the 2:1 resonance, while planets c and d appear close to a 5:3 period commensurability, although model degeneracy meant we were unable to retrieve robust TTV masses. Their inflated radii, likely due to extended H-He atmospheres, combined with low insolation makes all three planets excellent candidates for future comparative transmission spectroscopy with JWST.