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

Abstract

Context: TOI-2076 is a transiting three-planet system of sub-Neptunes orbiting a bright (G = 8.9 mag), young ($340\pm 80$ 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 $P=21.01538_{-0.00074}^{+0.00084}$ 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 $P=35.12537\pm 0.00067$ d alias. These observations also improved the radius precision of all three sub-Neptunes to $2.518\pm 0.036$, $3.497\pm 0.043$, and $3.232\pm 0.063$ $R_{\oplus }$. 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.

18 pages, 7 figure, 8 tables. Accepted for publication in Astronomy & Astrophysics. Photometry available on CDS/Vizier. Python package presented for modelling duotransiting planet candidates available at https://github.com/hposborn/MonoTools. Modelling & figure-creation code available at https://github.com/hposborn/TOI2076

References in corpus (41)

• The Transiting Exoplanet Survey Satellite
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• The TESS Objects of Interest Catalog from the TESS Prime Mission
• A new code for automatic determination of equivalent widths: Automatic Routine for line Equivalent widths in stellar Spectra (ARES)
• The CHEOPS mission
• CLES, Code Liegeois d'Evolution Stellaire
• A planet within the debris disk around the pre-main-sequence star AU Microscopii
• ARES v2 - new features and improved performance
• exoplanet: Gradient-based probabilistic inference for exoplanet data & other astronomical time series
• Six transiting planets and a chain of Laplace resonances in TOI-178
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• TTVFast: An efficient and accurate code for transit timing inversion problems
• The Photoeccentric Effect and Proto-Hot Jupiters I. Measuring photometric eccentricities of individual transiting planets
• Revising the ages of planet-hosting stars
• TESS Hunt for Young and Maturing Exoplanets (THYME) II: A 17 Myr Old Transiting Hot Jupiter in the Sco-Cen Association
• SPECULOOS -- Ultracool Dwarf Transit Survey: Target List and Strategy
• A super-Earth and a sub-Neptune orbiting the bright, quiet M3 dwarf TOI-1266
• TESS Hunt for Young and Maturing Exoplanets (THYME) III: a two-planet system in the 400 Myr Ursa Major Group
• Transit detection of the long-period volatile-rich super-Earth ${\nu }^2$ Lupi d with $CHEOPS$
• CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii
• TESS delivers its first Earth-sized planet and a warm sub-Neptune
• Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using pycheops
• WASP-186 and WASP-187: two hot Jupiters discovered by SuperWASP and SOPHIE with additional observations by TESS
• Discrepancies between isochrone fitting and gyrochronology for exoplanet host stars?
• The GAPS Programme at TNG XXI -- A GIARPS case-study of known young planetary candidates: confirmation of HD 285507 b and refutation of AD Leo b
• TESS Hunt for Young and Maturing Exoplanets (THYME) IV: Three small planets orbiting a 120 Myr-old star in the Pisces--Eridanus stream
• Reinvestigating $\alpha$ Cen AB in light of asteroseismic forward and inverse methods
• The age-mass-metallicity-activity relation for solar-type stars: Comparisons with asteroseismology and the NGC 188 open cluster
• TOI-2076 and TOI-1807: Two young, comoving planetary systems within 50 pc identified by TESS that are ideal candidates for further follow-up
• Uncovering the true periods of the young sub-Neptunes orbiting TOI-2076
• TESS Reveals a Short-period Sub-Neptune Sibling (HD 86226c) to a Known Long-period Giant Planet
• A sub-Neptune and a non-transiting Neptune-mass companion unveiled by ESPRESSO around the bright late-F dwarf HD 5278 (TOI-130)
• Transits of Known Planets Orbiting a Naked-Eye Star
• Alleviating the transit timing variation bias in transit surveys. I. RIVERS: Method and detection of a pair of resonant super-Earths around Kepler-1705
• A transit timing variation observed for the long-period extremely low density exoplanet HIP 41378f
• TOI-2257 b: A highly eccentric long-period sub-Neptune transiting a nearby M dwarf
• An extremely low-density and temperate giant exoplanet
• Resolving period aliases for TESS monotransits recovered during the extended mission
• CHEOPS observations of TESS primary mission monotransits
• Constraining Orbital Periods from Nonconsecutive Observations: Period Estimates for Long-Period Planets in Six Systems Observed by K2 During Multiple Campaigns

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• The TESS-Keck Survey. XV. Precise Properties of 108 TESS Planets and Their Host Stars
• The SOPHIE search for northern extrasolar planets-XIX. A system including a cold sub-Neptune potentially transiting a V = 6.5 star HD88986
• NEID Reveals that The Young Warm Neptune TOI-2076 b Has a Low Obliquity
• The TEMPO Survey I: Predicting Yields of the Transiting Exosatellites, Moons, and Planets from a 30-day Survey of Orion with the Nancy Grace Roman Space Telescope
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• The GAPS Programme at TNG. LIX. A characterisation study of the $\sim$300 Myr old multi-planetary system orbiting the star BD+40 2790 (TOI-2076)
• Homogeneous search for spot transits in Kepler and TESS photometry of K $-$ M-type main-sequence stars
• Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946
• An Adolescent and Near-Resonant Planetary System Near the End of Photoevaporation
• The multi-planet system TOI-5624: Four transiting sub-Neptunes with an outer companion revealed by transit-timing variations
• Uncovering the Rapidly Evolving Orbits of the Dynamic TOI-201 System
• A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf From K2
• KRONOS I: The $1-2.8\mu$m JWST Transmission Spectrum of the 23 Myr V1298 Tau c
• Validating the Orbital Periods of the Coolest TESS Exoplanet Candidates