Uncovering the true periods of the young sub-Neptunes orbiting TOI-2076
Creators: name: Osborn, Hugh P.
name: Bonfanti, Andrea
name: Gandolfi, Davide
name: Hedges, Christina
name: Leleu, Adrien
name: Fortier, Andrea
name: Futyan, David
name: Gutermann, Pascal
name: Maxted, Pierre F. L.
name: Borsato, Luca
name: Collins, Karen A.
name: da Silva, J. Gomes
name: Chew, Yilen Gómez Maqueo
name: Hooton, Matthew J.
name: Lendl, Monika
name: Parviainen, Hannu
name: Salmon, Sébastien
name: Schanche, Nicole
name: Serrano, Luisa M.
name: Sousa, Sergio G.
name: Tuson, Amy
name: Ulmer-Moll, Solène
name: Van Grootel, Valerie
name: Wells, R. D.
name: Wilson, Thomas G.
name: Alibert, Yann
name: Alonso, Roi
name: Anglada, Guillem
name: Asquier, Joel
name: Navascues, David Barrado y
name: Baumjohann, Wolfgang
name: Beck, Thomas
name: Benz, Willy
name: Biondi, Federico
name: Bonfils, Xavier
name: Bouchy, Francois
name: Brandeker, Alexis
name: Broeg, Christopher
name: Bárczy, Tamas
name: Barros, S. C. C.
name: Cabrera, Juan
name: Charnoz, Sébastien
name: Cameron, Andrew Collier
name: Csizmadia, Szilard
name: Davies, Melvyn B.
name: Deleuil, Magali
name: Delrez, Laetitia
name: Demory, Brice-Olivier
name: Ehrenreich, David
name: Erikson, Anders
name: Fossati, Luca
name: Fridlund, Malcolm
name: Gillon, Michaël
name: Gómez-Muñoz, M. A.
name: Güdel, Manuel
name: Heng, Kevin
name: Hoyer, Sergio
name: Isaak, Kate G.
name: Kiss, Laszlo
name: Laskar, Jacques
name: Etangs, Alain Lecavelier des
name: Lovis, Christophe
name: Magrin, Demetrio
name: Malavolta, Luca
name: McCormac, James
name: Nascimbeni, Valerio
name: Olofsson, Göran
name: Ottensamer, Roland
name: Pagano, Isabella
name: Pallé, Enric
name: Peter, Gisbert
name: Piazza, Daniele
name: Piotto, Giampaolo
name: Pollacco, Don
name: Queloz, Didier
name: Ragazzoni, Roberto
name: Rando, Nicola
name: Rauer, Heike
name: Reimers, Christian
name: Ribas, Ignasi
name: Demangeon, Olivier D. S.
name: Smith, Alexis M. S.
name: Sabin, L.
name: Santos, Nuno
name: Scandariato, Gaetano
name: Schroffenegger, U.
name: Schwarz, Rick P.
name: Shporer, Avi
name: Simon, Attila E.
name: Steller, Manfred
name: Szabó, Gyula M.
name: Ségransan, Damien
name: Thomas, Nicolas
name: Udry, Stéphane
name: Walter, Ingo
name: Walton, Nicholas
Publisher: name: arXiv
Year: 2022
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Context: TOI-2076 is a transiting three-planet system of sub-Neptunes orbiting a bright (G = 8.9 mag), young ($340\pm80$ 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 $P=21.01538^{+0.00084}_{-0.00074}$ 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 $P=35.12537\pm0.00067$ d alias. These observations also improved the radius precision of all three sub-Neptunes to $2.518\pm0.036$, $3.497\pm0.043$, and $3.232\pm0.063$ $R_\oplus$. 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.
description: 18 pages, 7 figure, 8 tables. Accepted for publication in Astronomy &amp; Astrophysics. Photometry available on CDS/Vizier. Python package presented for modelling duotransiting planet candidates available at https://github.com/hposborn/MonoTools. Modelling &amp; figure-creation code available at https://github.com/hposborn/TOI2076