TOI-757 b: An Eccentric Transiting Mini-Neptune On Aa 17.5-d Orbit

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 Rp=2.5±0.1R_⊕ and a mass of Mp=10.5+2.2−2.1M_⊕, implying a bulk density of ρp=3.6±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.

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 Etangs, 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 et al. (32 additional authors not shown)

Comments: Accepted for publication in MNRAS; 26 pages, 14 figures, 6 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2407.20525 [astro-ph.EP](or arXiv:2407.20525v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2407.20525
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Submission history
From: Ahlam Alqasim
[v1] Tue, 30 Jul 2024 03:56:04 UTC (6,984 KB)
https://arxiv.org/abs/2407.20525
Astrobiology, Exoplanet,