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., 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., …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
• Electronic ISSN: 1365-2966
• 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