TOI−757 b:an eccentric transiting mini−Neptune on a 17.5−d orbit

• DOI: 10.17615/gser-4n45
• Publication Date: 2024-07-31
• Authors: A Alqasim; N Grieves; N M Rosário; D Gandolfi; J H Livingston; S Sousa; K A Collins; J K Teske; M Fridlund; J A Egger; J Cabrera; C Hellier; A F Lanza; V Van Eylen; F Bouchy; R J Oelkers; G Srdoc; S Shectman; M Günther; E Goffo; T Wilson; L M Serrano; A Brandeker; S X Wang; A Heitzmann; A Bonfanti; L Fossati; Y Alibert; L Delrez; R Sefako; S Barros; K I Collins; O D S Demangeon; S H Albrecht; R Alonso; J Asquier; T Barczy; D Barrado; W Baumjohann; T Beck; W Benz; N Billot; L Borsato; C Broeg; E M Bryant; R P Butler; W D Cochran; A Collier Cameron; A C M Correia; J D Crane; Sz Csizmadia; P E Cubillos; M B Davies; T Daylan; M Deleuil; A Deline; B -O Demory; A Derekas; B Edwards; D Ehrenreich; A Erikson; Z Essack; A Fortier; K Gazeas; M Gillon; M Gudel; J Hasiba; A P Hatzes; Ch Helling; T Hirano; S B Howell; S Hoyer; K G Isaak; J M Jenkins; S Kanodia; L L Kiss; J Korth; K W F Lam; J Laskar; A Lecavelier des ...; M Lendl; M B Lund; R Luque; A W Mann; D Magrin; P F L Maxted; C Mordasini; N Narita; V Nascimbeni; G Nowak; G Olofsson; H P Osborn; H L M Osborne; D Osip; R Ottensamer; I Pagano; E Palle; G Peter; G Piotto; D Pollacco; D Queloz; R Ragazzoni; N Rando; H Rauer; S Redfield; I Ribas; M Rice; G R Ricker; M Rieder; S Salmon; N C Santos; G Scandariato; S Seager; D Segransan; A Shporer; A E Simon; A M S Smith; M Stalport; Gy M Szabo; I Thompson; J D Twicken; S Udry; R Vanderspek; V Van Grootel; J Venturini; E Villaver; J Villaseñor; V Viotto; I Walter; N A Walton; J N Winn; S W Yee
• Keywords: techniques: photometric – techniques: radial velocities – planets and satellites: composition – planets and satellites: interiors – stars: individual: TOI-757 (TIC 130924120).; 103003 Astronomie; FOS: Physical sciences; 103038 Weltraumforschung; [SDU] Sciences of the Universe [physics]; 103003 Astronomy; techniques: photometric; 103038 Space exploration; techniques: radial velocities; QB Astronomy; 103004 Astrophysics; stars: individual: TOI-757 (TIC 130924120); QB; MCC; Earth and Planetary Astrophysics (astro-ph.EP); radial velocities [Techniques]; photometric [Techniques]; planets and satellites: composition; DAS; 103004 Astrophysik; interiors [Planets and satellites]; 520; planets and satellites: interiors; individual: TOI-757 (TIC 130924120) [Stars]; [SDU]Sciences of the Universe [physics]; composition [Planets and satellites]; Astronomie und zugeordnete Wissenschaften; Astrophysics - Earth and Planetary Astrophysics

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 $R_{\mathrm{p}} = 2.5 \pm 0.1 R_{\oplus }$ and a mass of $M_{\mathrm{p}} = 10.5^{+2.2}_{-2.1} M_{\oplus }$, implying a bulk density of $\rho _{\text{p}} = 3.6 \pm 0.8$ 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.