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Uncovering the true periods of the young sub-Neptunes orbiting TOI-2076

H. P. Osborn, A. Bonfanti, D. Gandolfi, C. Hedges, A. Leleu, A. Fortier, D. Futyan, P. Guterman, P. F. L. Maxted, L. Borsato, K. A. Collins, J. Gomes da Silva, Y. Gómez Maqueo Chew, M. J. Hooton, M. Lendl, H. Parviainen, S. Salmon, N. Schanche, L. M. Serrano, S. G. Sousa, A. Tuson, S. Ulmer-Moll, V. Van Grootel, R. D. Wells, T. G. Wilson, Y. Alibert, R. Alonso, G. Anglada-Escude, J. Asquier, D. Barrado-Navascues, W. Baumjohann, T. Beck, W. Benz, F. Biondi, X. Bonfils, F. Bouchy, A. Brandeker, C. Broeg, T. Bárczy, S. C. C. Barros, J. Cabrera, S. Charnoz, A. Collier Cameron, Sz. Csizmadia, M. B. Davies, M. Deleuil, L. Delrez, B.-O. Demory, D. Ehrenreich, A. Erikson, L. Fossati, M. Fridlund, M. Gillon, M. A. Gömez-Munoz, M. Güdel, K. Heng, S. Hoyer, K. G Isaak, L. L. Kiss, J. Laskar, A. Lecavelier Des Etangs, C. Lovis, D. Magrin, L. Malavolta, J. McCormac, 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, C. Reimers, I. Ribas, O. Demangeon, A. M. S. Smith, L. Sabin, N. C. Santos, G. Scandariato, U. Schroffenegger, R. P. Schwarz, A. Shporer, A. E. Simon, M. Steller, Gy. M. Szabó, D. Ségransan, N. Thomas, S. Udry, I. Walter, N. A. Walton

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.

planets and satellites: detection / stars: individual: TOI-2076 / techniques: photometric

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Astronomy & Astrophysics
Volume 664, Article Number A156, Number of pages 17
2022 August

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia