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

Alqasim, A; Grieves, N; Rosário, N M; Gandolfi, D; Livingston, J H; Sousa, S; Collins, K A; Teske, J K; Fridlund, M; Egger, J A; Cabrera, J; Hellier, C; Lanza, A F; Van Eylen, V; Bouchy, F; Oelkers, R J; Srdoc, G; Shectman, S; Günther, M; Goffo, E; Wilson, T; Serrano, L M; Brandeker, A; Wang, S X; Heitzmann, A; Bonfanti, A; Fossati, L; Alibert, Y; Delrez, L; Sefako, R; Barros, S; Collins, K I; Demangeon, O D S; Albrecht, S H; Alonso, R; Asquier, J; Barczy, T; Barrado, D; Baumjohann, W; Beck, T; Benz, W; Billot, N; Borsato, L; Broeg, C; Bryant, E M; Butler, R P; Cochran, W D; Cameron, A Collier; Correia, A C M; Crane, J D; Csizmadia, Sz; Cubillos, P E; Davies, M B; Daylan, T; Deleuil, M; Deline, A; Demory, B -O; Derekas, A; Edwards, B; Ehrenreich, D; Erikson, A; Essack, Z; Fortier, A; Gazeas, K; Gillon, M; Gudel, M; Hasiba, J; Hatzes, A P; Helling, Ch; Hirano, T; Howell, S B; Hoyer, S; Isaak, K G; Jenkins, J M; Kanodia, S; Kiss, L L; Korth, J; Lam, K W F; Laskar, J; Etangs, A Lecavelier...

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.

Citation

Alqasim, A., Grieves, N., Rosário, N. M., Gandolfi, D., Livingston, J. H., Sousa, S., …Yee, S. W. (2024). TOI–757 b: an eccentric transiting mini–Neptune on a 17.5–d orbit. Monthly Notices of the Royal Astronomical Society, 533(1), 1-26. https://doi.org/10.1093/mnras/stae1767

• Journal Article Type: Article
• Acceptance Date: Jul 7, 2024
• Online Publication Date: Jul 31, 2024
• Publication Date: Aug 7, 2024
• Deposit Date: Aug 27, 2024
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 533
• Issue: 1
• Pages: 1-26
• DOI: https://doi.org/10.1093/mnras/stae1767
• Public URL: https://keele-repository.worktribe.com/output/888178
• Publisher URL: https://academic.oup.com/mnras/article/533/1/1/7725072