ASTEP confirmation of a pair of long-period Jupiter-sized planets with extremely low densities transiting TOI-791

Abstract

Gas giant planets with periods $20<P<300\mathrm{days}$ orbiting Sun-like stars are a relatively uncommon outcome of planetary formation, and key questions about the nature and formation of this sub-population remain unanswered. Theoretical models for the location of their formation (in- or ex-situ) and for their subsequent migration predict different outcomes in terms of planet masses and eccentricities, indicating that observations have a key role to play in disentangling their histories. In this work we present the discovery and confirmation of a pair of long-period Jupiter-sized planets transiting an F7 star: TOI-791 b is a $0.993\pm 0.033{\mathrm{R}}_{\mathrm{Jup}}$ planet on a $139.29931_{-0.00012}^{+0.00011}\mathrm{day}$ orbit, and TOI-791 c, a $1.155\pm 0.040{\mathrm{R}}_{\mathrm{Jup}}$ planet on a $232.01570_{-0.00071}^{+0.00067}\mathrm{day}$ orbit. The two planets are within 0.07% of a second-order 5:3 period commensurability leading to transit timing variations (TTVs) of up to 50 minutes. We confirm their planetary nature using ground-based photometry, including multiple full detections of the $>11\mathrm{hr}$ transits of both TOI-791 b and c from Antarctica with ASTEP, making these the longest-duration transits ever observed in their entirety from the ground. Our detailed analysis of the TTV signal allows us to measure dynamical masses for both planets, which yield densities of ${\rho }_{\mathrm{b}}=0.038\pm 0.008\mathrm{g}\mathrm{c}{\mathrm{m}}^{-3}$ and ${\rho }_{\mathrm{c}}=0.047\pm 0.006\mathrm{g}\mathrm{c}{\mathrm{m}}^{-3}$, indicating that TOI-791~b and c are two of the lowest density giant planets ever detected. While these measurements are robust, further follow-up is needed to fully characterise the TTV signal and the architecture of the system.

22 pages, 18 figures, Published in MNRAS

References in corpus (47)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The Transiting Exoplanet Survey Satellite
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• The TESS Objects of Interest Catalog from the TESS Prime Mission
• Modern stellar spectroscopy caveats
• The CHEOPS mission
• Towards Chemical Constraints on Hot Jupiter Migration
• Parallax Systematics and Photocenter Motions of Benchmark Eclipsing Binaries in Gaia EDR3
• CERES: A Set of Automated Routines for Echelle Spectra
• Eclipsing Binary Stars as Benchmarks for Trigonometric Parallaxes in the Gaia Era
• Tracing the formation history of giant planets in protoplanetary disks with Carbon, Oxygen, Nitrogen and Sulphur
• Empirical, Accurate Masses and Radii of Single Stars with TESS and Gaia
• Can giant planets form by gravitational fragmentation of discs?
• Cool Jupiters greatly outnumber their toasty siblings: Occurrence rates from the Anglo-Australian Planet Search
• Beyond Equilibrium Temperature: How the Atmosphere/Interior Connection Affects the Onset of Methane, Ammonia, and Clouds in Warm Transiting Giant Planets
• Minimum Core Masses for Giant Planet Formation With Realistic Equations of State and Opacities
• Measurement of planet masses with transit timing variations due to synodic "chopping" effects
• Speckle Observations of TESS Exoplanet Host Stars. II. Stellar Companions at 1-1000 AU and Implications for Small Planet Detection
• The PLATO field selection process I. Identification and content of the long-pointing fields
• The Densities of Planets in Multiple Stellar Systems
• A Tendency Toward Alignment in Single-Star Warm Jupiter Systems
• prose: A Python framework for modular astronomical images processing
• Speckle Imaging Excludes Low-Mass Companions Orbiting the Exoplanet Host Star TRAPPIST-1
• TOI-677 b: A Warm Jupiter (P=11.2d) on an eccentric orbit transiting a late F-type star
• Unresolved Binary Exoplanet Host Stars Fit as Single Stars: Effects on the Stellar Parameters
• Planet Hunters TESS II: Findings from the first two years of TESS
• A transiting warm giant planet around the young active star TOI-201
• Can planetary rings explain the extremely low density of HIP 41378f?
• TOI-481 b & TOI-892 b: Two long period hot Jupiters from the Transiting Exoplanet Survey Satellite
• Spectroscopic parameters for solar-type stars with moderate/high rotation. New parameters for 10 planet-hosts
• An Integrable Model for the Dynamics of Planetary Mean Motion Resonances
• A semi-empirical model for magnetic braking of solar-type stars
• A Highly Eccentric Warm Jupiter Orbiting TIC 237913194
• A pair of warm giant planets near the 2:1 mean motion resonance around the K-dwarf star TOI-2202
• TOI-2525 b and c: A pair of massive warm giant planets with a strong transit timing variations revealed by TESS
• Unbiasing the density of TTV-characterised sub-Neptunes: Update of the mass-radius relationship of 34 Kepler planets
• A transit timing variation observed for the long-period extremely low density exoplanet HIP 41378f
• Three long period transiting giant planets from TESS
• HD 28109 hosts a trio of transiting Neptunian planets including a near-resonant pair, confirmed by ASTEP from Antarctica
• An extremely low-density and temperate giant exoplanet
• Measuring the Obliquities of the TRAPPIST-1 Planets with MAROON-X
• A Circumplanetary Dust Ring May Explain the Extreme Spectral Slope of the 10 Myr Young Exoplanet K2-33b
• Observing exoplanets from Antarctica in two colours: Set-up and operation of ASTEP+
• Mutual Occurrence Ratio of Planets. I. New Clues to Reveal Origins of Hot- and Warm-Jupiter from the RV Sample
• The star HIP 41378 potentially misaligned with its cohort of long-period planets