TOI−757 b: an eccentric transiting mini−Neptune on a 17.5−d orbit
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2024-09
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Journal Article
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Abstract
We report the spectroscopic confirmation and fundamental properties of TOI−757 b, a mini−Neptune on a 17.5−d orbit transiting a bright star (V = 9.7 mag) discovered by the TESS mission. We acquired high−precision radial velocity measurements with the HARPS, ESPRESSO, and PFS spectrographs to confirm the planet detection and determine its mass. We also acquired space−borne transit photometry with the CHEOPS space telescope to place stronger constraints on the planet radius, supported with ground−based LCOGT photometry. WASP and KELT photometry were used to help constrain the stellar rotation period. We also determined the fundamental parameters of the host star. We find that TOI−757 b has a radius of Rₚ = 2.5 ± 0.1R⊕ and a mass of Mp = 10.5⁺².²₋₂.₁M⊕, implying a bulk density of ρₚ = 3.6 ± 0.8 g cm⁻³. Our internal composition modelling was unable to constrain the composition of TOI−757 b, highlighting the importance of atmospheric observations for the system. We also find the planet to be highly eccentric with e = 0.39⁺⁰.⁰⁸₋₀.₀₇, making it one of the very few highly eccentric planets among precisely characterized mini−Neptunes. Based on comparisons to other similar eccentric systems, we find a likely scenario for TOI−757 b’s formation to be high eccentricity migration due to a distant outer companion. We additionally propose the possibility of a more intrinsic explanation for the high eccentricity due to star−star interactions during the earlier epoch of the Galactic disc formation, given the low metallicity and older age of TOI−757.
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published
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Volume
533 (1)
Pages / Article No.
1 - 26
Publisher
Oxford University Press
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Subject
techniques: photometric; techniques: radial velocities; planets and satellites: composition; planets and satellites: interiors; stars: individual: TOI-757 (TIC 130924120)
Organisational unit
09754 - Queloz, Didier / Queloz, Didier
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Funding
182901 - NCCR PlanetS P1.1 Extension (SNF)
205606 - NCCR PlanetS / Externship M.R. (SNF)
205606 - NCCR PlanetS / Externship M.R. (SNF)