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

• Published in: arXiv.org
• Main Authors: Grieves, N, Gandolfi, D, Livingston, J H, Sousa, S, Collins, K A, Teske, J K, Fridlund, M, Egger, J A, Cabrera, J, Lanza, A F, V Van Eylen, Bouchy, F, Oelkers, R J, Srdoc, G, Shectman, S, Günther, M, Goffo, E, Wilson, T, Serrano, L M, Heitzmann, A, Bonfanti, A, Fossati, L, Alibert, Y, Delrez, L, Sefako, R, Barros, S, Collins, K I, Albrecht, S H, Alonso, R, Asquier, J, Barrado, D, Beck, T, Benz, W, Billot, N, Borsato, L, Broeg, C, Bryant, E M, Butler, R P, Cochran, W D, A Collier Cameron, Csizmadia, Sz, Cubillos, P E, Davies, M B, Daylan, T, Deleuil, M, Deline, A, B -O Demory, Edwards, B, Ehrenreich, D, Erikson, A, tier, A, Gazeas, K, Gillon, M, Hasiba, J, Helling, Ch, Hirano, T, Hoyer, S, Isaak, K G, Jenkins, J M, Kanodia, S, Kiss, L L, Korth, J, Lam, K W F, A Lecavelier des Etangs, Lendl, M, Lund, M B, Luque, R, Mann, A W, Mordasini, C, Narita, N, Nascimbeni, V, Nowak, G, Olofsson, G, Osborne, H L M, Osip, D, Pagano, I, Palle, E, Peter, G, Pollacco, D, Queloz, D, Ragazzoni, R, Rauer, H, Redfield, S, Rice, M, Ricker, G R, Rieder, M, Scandariato, G, Seager, S, Segransan, D, Shporer, A, Simon, A E, Smith, A M S, Szabo, Gy M, Udry, S, Vanderspek, R, V Van Grootel, Villaver, E, Villaseñor, J, Walter, I, Walton, N A
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 30.07.2024
• Subjects: Bulk density; Galactic disk; Metallicity; Photometry; Planet detection; Planetary composition; Planetary rotation; Radial velocity; Space telescopes; Spectrographs; Stellar rotation
• ISSN: 2331-8422

We report the spectroscopic confirmation and fundamental properties of TOI-757 b, a mini-Neptune on a 17.5-day 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 modeling 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 disk formation, given the low metallicity and older age of TOI-757.