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. Gutermann (1) , 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 , J. Asquier , D. Barrado y Navascues , W. Baumjohann , T. Beck , W. Benz , F. Biondi , X. Bonfils (2) , F. Bouchy , A. Brandeker , C. Broeg , T. Bárczy , S. C. C. Barros , J. Cabrera , S. Charnoz (3) , A. Collier Cameron , S. Csizmadia , M. B. Davies , M. Deleuil (1) , 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 (1) , K. G. Isaak , L. Kiss , J. Laskar (4) , A. Lecavelier Des Etangs (5) , 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. D. S. Demangeon , A. M. S. Smith , L. Sabin , N. Santos , G. Scandariato , U. Schroffenegger , R. P. Schwarz , A. Shporer , A. E. Simon , M. Steller , G. M. Szabó , D. Ségransan , N. Thomas , S. Udry , I. Walter , N. Walton

1 LAM - Laboratoire d'Astrophysique de Marseille
2 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
3 IPGP (UMR_7154) - Institut de Physique du Globe de Paris
4 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
5 IAP - Institut d'Astrophysique de Paris

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.

Photometric time series are only available at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/664/A156

Mots clés: planets and satellites: detection; stars: individual: TOI-2076; techniques: photometric; Astrophysics - Earth and Planetary Astrophysics

Domaines: Planète et Univers [physics]; Astrophysique [astro-ph]

H. P. Osborn, A. Bonfanti, D. Gandolfi, C. Hedges, A. Leleu, et al.. Uncovering the true periods of the young sub-Neptunes orbiting TOI-2076. Astronomy and Astrophysics - A&A, 2022, 664, ⟨10.1051/0004-6361/202243065⟩. ⟨insu-03776410⟩