L. Thomas, G. Hébrard, H. Kellermann, J. Korth, N. Heidari, T. Forveille, S. G. Sousa, L. Schöller, A. Riffeser, C. Gössl, J. Serrano Bell, F. Kiefer, N. Hara, F. Grupp, J. Ehrhardt, F. Murgas, K. A. Collins, A. Bieryla, H. Parviainen, A. A. Belinski, E. Esparza-Borges, D. R. Ciardi, C. A. Clark, A. Fukui, E. A. Gilbert, U. Hopp, K. Ikuta, J. M. Jenkins, D. W. Latham, N. Narita, L. D. Nielsen, S. N. Quinn, E. Palle, J. Pippert, A. S. Polanski, C. Ries, M. Schmidt, R. P. Schwarz, S. Seager, I. A. Strakhov, S. Striegel, J. C. van Eyken, N. Watanabe, C. N. Watkins, J. N. Winn, C. Ziegler, R. Zöller
Abstract
We report the discovery and characterization of two sub-Saturns from the Transiting Exoplanet Survey Satellite (TESS) using high- resolution spectroscopic observations from the MaHPS spectrograph at the Wendelstein Observatory and the SOPHIE spectrograph at the Haute-Provence Observatory. Combining photometry from TESS, KeplerCam, LCOGT, and MuSCAT2, along with the radial velocity measurements from MaHPS and SOPHIE, we measured precise radii and masses for both planets. TOI-5108 b is a sub-Saturn, with a radius of 6.6 ± 0.1 R⊕ and a mass of 32 ± 5 M⊕. TOI-5786 b is similar to Saturn, with a radius of 8.54 ± 0.13 R⊕ and a mass of 73 ± 9 M⊕. The host star for TOI-5108 b is a moderately bright (Vmag 9.75) G-type star. TOI-5786 is a slightly dimmer (Vmag 10.2) F-type star. Both planets are close to their host stars, with periods of 6.75 days and 12.78 days, respectively. This puts TOI-5108 b just within the bounds of the Neptune desert, while TOI-5786 b is right above the upper edge. We estimated hydrogen-helium (H/He) envelope mass fractions of 38% for TOI-5108 b and 74% for TOI-5786 b. However, when using a model for the interior structure that includes tidal effects, the envelope fraction of TOI-5108 b could be much lower (~20%), depending on the obliquity. We estimated mass-loss rates between 1.0 x 109 g/s and 9.8 x 109 g/s for TOI-5108 b and between 3.6 x 108 g/s and 3.5 x 109 g/s for TOI-5786 b. Given their masses, both planets could be stable against photoevaporation. Furthermore, at these mass-loss rates, there is likely no detectable signal in the metastable helium triplet with the James Webb Space Telescope (JWST). We also detected a transit signal for a second planet candidate in the TESS data of TOI-5786, with a period of 6.998 days and a radius of 3.83 ± 0.16 R⊕. Using our RV data and photodynamical modeling, we were able to provide a 3-σ upper limit of 26.5 M⊕ for the mass of the potential inner companion to TOI-5786 b.
Keywords
techniques: photometric / techniques: radial velocities / planets and satellites: detection / planetary systems / planets and satellites: gaseous planets
Astronomy & Astrophysics
Volume 694, Article Number A143, Number of pages 23
2025 February
