Bibcode
Thomas, Luis; Hébrard, Guillaume; Kellermann, Hanna; Korth, Judith; Heidari, Neda; Forveille, Thierry; Sousa, Sérgio G.; Schöller, Laura; Riffeser, Arno; Gössl, Claus; Serrano Bell, Juan; Kiefer, Flavien; Hara, Nathan; Grupp, Frank; Ehrhardt, Juliana; Murgas, Felipe; Collins, Karen A.; Bieryla, Allyson; Parviainen, Hannu; Belinski, Alexandr A.; Esparza-Borges, Emma; Ciardi, David R.; Clark, Catherine A.; Fukui, Akihiko; Gilbert, Emily A.; Hopp, Ulrich; Ikuta, Kai; Jenkins, Jon M.; Latham, David W.; Narita, Norio; Nielsen, Louise D.; Quinn, Samuel N.; Palle, Enric; Pippert, Jan-Niklas; Polanski, Alex S.; Ries, Christoph; Schmidt, Michael; Schwarz, Richard P.; Seager, Sara; Strakhov, Ivan A.; Striegel, Stephanie; van Eyken, Julian C.; Watanabe, Noriharu; Watkins, Cristilyn N.; Winn, Joshua N.; Ziegler, Carl; Zöller, Raphael
Bibliographical reference
Astronomy and Astrophysics
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2
2025
Journal
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0
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0
Description
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.