TOI–757 b: an eccentric transiting mini–Neptune on a 17.5–d orbit
Creators: name: Alibert, Y
name: Shporer, A
name: Serrano, L M
name: Gandolfi, D
name: Benz, W
name: Gazeas, K
name: Srdoc, G
name: Winn, J N
name: Cubillos, P E
name: Nascimbeni, V
name: Simon, A E
name: Walton, N A
name: Palle, E
name: Ricker, G R
name: Howell, S B
name: Sousa, S
name: Ehrenreich, D
name: Billot, N
name: Szabo, Gy M
name: Scandariato, G
name: Alonso, R
name: Fossati, L
name: Queloz, D
name: Demory, B -O
name: Erikson, A
name: Delrez, L
name: Pagano, I
name: Isaak, K G
name: Rando, N
name: Hoyer, S
name: Sefako, R
name: Rosário, N M
name: Cameron, A Collier
name: Kiss, L L
name: Ragazzoni, R
name: Grieves, N
name: Ribas, I
name: Van Grootel, V
name: Gillon, M
name: Hasiba, J
name: Lam, K W F
name: Smith, A M S
name: Viotto, V
name: Brandeker, A
name: Davies, M B
name: Laskar, J
name: Edwards, B
name: Gudel, M
name: Oelkers, R J
name: Santos, N C
name: Barros, S
name: Narita, N
name: Hirano, T
name: Goffo, E
name: Vanderspek, R
name: Bryant, E M
name: Osborn, H P
name: Udry, S
name: Bouchy, F
name: Lund, M B
name: Walter, I
name: Korth, J
name: Hellier, C
name: Günther, M
name: Rice, M
name: Luque, R
name: Cabrera, J
name: Seager, S
name: Alqasim, A
name: Csizmadia, Sz
name: Hatzes, A P
name: Borsato, L
name: Rieder, M
name: Collins, K I
name: Wang, S X
name: Daylan, T
name: Albrecht, S H
name: Thompson, I
name: Deline, A
name: Derekas, A
name: Lanza, A F
name: Demangeon, O D S
name: Helling, Ch
name: Ottensamer, R
name: Olofsson, G
name: Twicken, J D
name: Beck, T
name: Mann, A W
name: Segransan, D
name: Broeg, C
name: Etangs, A Lecavelier des
name: Collins, K A
name: Salmon, S
name: Maxted, P F L
name: Fortier, A
name: Heitzmann, A
name: Egger, J A
name: Deleuil, M
name: Crane, J D
name: Pollacco, D
name: Fridlund, M
name: Barrado, D
name: Butler, R P
name: Yee, S W
name: Jenkins, J M
name: Rauer, H
name: Correia, A C M
name: Barczy, T
name: Shectman, S
name: Osip, D
name: Asquier, J
name: Baumjohann, W
name: Kanodia, S
name: Redfield, S
name: Wilson, T
name: Teske, J K
name: Villaseñor, J
name: Mordasini, C
name: Peter, G
name: Nowak, G
name: Bonfanti, A
name: Osborne, H L M
name: Essack, Z
name: Cochran, W D
name: Van Eylen, V
name: Villaver, E
name: Piotto, G
name: Stalport, M
name: Magrin, D
name: Lendl, M
name: Livingston, J H
name: Venturini, J
Publisher: name: Oxford University Press (OUP)
Year: 2024

description: 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.