Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N and TESS

Abstract

We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data with TESS and CHEOPS photometry, and a new set of $62$ HARPS-N radial velocities (RVs). Our joint analysis confirms the presence of four transiting planets, namely TOI-561 b ($P=0.45$ d, $R=1.42$ R${}_{\oplus }$, $M=2.0$ M${}_{\oplus }$), c ($P=10.78$ d, $R=2.91$ R${}_{\oplus }$, $M=5.4$ M${}_{\oplus }$), d ($P=25.7$ d, $R=2.82$ R${}_{\oplus }$, $M=13.2$ M${}_{\oplus }$) and e ($P=77$ d, $R=2.55$ R${}_{\oplus }$, $M=12.6$ M${}_{\oplus }$). Moreover, we identify an additional, long-period signal ($>450$ d) in the RVs, which could be due to either an external planetary companion or to stellar magnetic activity. The precise masses and radii obtained for the four planets allowed us to conduct interior structure and atmospheric escape modelling. TOI-561 b is confirmed to be the lowest density (${\rho }_{\mathrm{b}}=3.8\pm 0.5$ g cm${}^{-3}$) ultra-short period (USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellar metallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certain amount of water. In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in addition to a possibly large water layer. The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets b and c having experienced significant gas loss, and planets d and e showing an atmospheric content consistent with the original one. The uniqueness of the USP planet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealing target for follow-up studies.

22 pages, 19 figures. Accepted for publication in MNRAS

References in corpus (34)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• The K2 Mission: Characterization and Early results
• Growth Model Interpretation of Planet Size Distribution
• Three regimes of extrasolar planets inferred from host star metallicities
• CLES, Code Liegeois d'Evolution Stellaire
• Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds
• A generalized bayesian inference method for constraining the interiors of super Earths and sub-Neptunes
• Six transiting planets and a chain of Laplace resonances in TOI-178
• Kepler Multi-Planet Systems Exhibit Unexpected Intra-system Uniformity in Mass and Radius
• On Correlated-noise Analyses Applied To Exoplanet Light Curves
• Revising the ages of planet-hosting stars
• Correcting the spectroscopic surface gravity using transits and asteroseismology. No significant effect on temperatures or metallicities with ARES+MOOG in LTE
• Constraining planet structure and composition from stellar chemistry: trends in different stellar populations
• From planetesimals to planets: volatile molecules
• Transit detection of the long-period volatile-rich super-Earth ${\nu }^2$ Lupi d with $CHEOPS$
• Radial Velocity Data Analysis with Compressed Sensing Techniques
• CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii
• CKS VIII: Eccentricities of Kepler Planets and Tentative Evidence of a High Metallicity Preference for Small Eccentric Planets
• WASP-186 and WASP-187: two hot Jupiters discovered by SuperWASP and SOPHIE with additional observations by TESS
• Reinvestigating $\alpha$ Cen AB in light of asteroseismic forward and inverse methods
• The HADES RV Programme with HARPS-N@TNG - GJ 3998: An early M-dwarf hosting a system of Super-Earths
• The Kepler-11 system: evolution of the stellar high-energy emission and {initial planetary} atmospheric mass fractions
• Close-in sub-Neptunes reveal the past rotation history of their host stars: atmospheric evolution of planets in the HD3167 and K2-32 planetary systems
• TKS X: Confirmation of TOI-1444b and a Comparative Analysis of the Ultra-short-period Planets with Hot Neptunes
• A transit survey to search for planets around hot subdwarfs: I. methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS
• An ultra-short period rocky super-Earth orbiting the G2-star HD 80653
• The EBLM project -- VIII. First results for M-dwarf mass, radius and effective temperature measurements using CHEOPS light curves
• On the stellar clustering and architecture of planetary systems
• The Detection of Earth-mass Planets around Active Stars: The Mass of Kepler-78b
• MCMCI: A code to fully characterise an exoplanetary system
• Bridging the Planet Radius Valley: Stellar Clustering as a Key Driver for Turning Sub-Neptunes into Super-Earths
• A CHEOPS White Dwarf Transit Search
• A hot mini-Neptune in the radius valley orbiting solar analogue HD 110113
• On the Orbital Spacing Pattern of Kepler Multiple Planet Systems

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• Characterisation of TOI-406 as showcase of the THIRSTEE program: A 2-planet system straddling the M-dwarf density gap
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