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TOI-5108 b and TOI 5786 b : Two transiting sub-Saturns detected and characterized with TESS, MaHPS, and SOPHIE

Thomas, Luis ; Hébrard, Guillaume ; Kellermann, Hanna ; Korth, Judith LU ; Heidari, Neda ; Forveille, Thierry ; Sousa, Sérgio G. ; Schöller, Laura ; Riffeser, Arno and Gössl, Claus , et al. (2025) In Astronomy and Astrophysics 694.
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... (More)

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 × 109 g/s and 9.8 × 109 g/s for TOI-5108 b and between 3.6 × 108 g/s and 3.5 × 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.

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publishing date
type
Contribution to journal
publication status
published
subject
keywords
Planetary systems, Planets and satellites: detection, Planets and satellites: gaseous planets, Techniques: photometric, Techniques: radial velocities
in
Astronomy and Astrophysics
volume
694
article number
A143
publisher
EDP Sciences
external identifiers
  • scopus:85217678197
ISSN
0004-6361
DOI
10.1051/0004-6361/202451676
language
English
LU publication?
yes
additional info
Publisher Copyright: © The Authors 2025.
id
2ccdcf7f-c30c-4399-8419-792135c7941e
date added to LUP
2025-06-24 13:24:35
date last changed
2025-06-24 13:25:00
@article{2ccdcf7f-c30c-4399-8419-792135c7941e,
  abstract     = {{<p>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<sub>⊕</sub> and a mass of 32 ± 5 M<sub>⊕</sub>. TOI-5786 b is similar to Saturn, with a radius of 8.54 ± 0.13 R<sub>⊕</sub> and a mass of 73 ± 9 M<sub>⊕</sub>. 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 × 10<sup>9</sup> g/s and 9.8 × 10<sup>9</sup> g/s for TOI-5108 b and between 3.6 × 10<sup>8</sup> g/s and 3.5 × 10<sup>9</sup> 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<sub>⊕</sub>. Using our RV data and photodynamical modeling, we were able to provide a 3-σ upper limit of 26.5 M<sub>⊕</sub> for the mass of the potential inner companion to TOI-5786 b.</p>}},
  author       = {{Thomas, Luis and Hébrard, Guillaume and Kellermann, Hanna and Korth, Judith and Heidari, Neda and Forveille, Thierry and Sousa, Sérgio G. and Schöller, Laura and Riffeser, Arno and Gössl, Claus and Serrano Bell, Juan and Kiefer, Flavien and Hara, Nathan and Grupp, Frank and Ehrhardt, Juliana and Murgas, Felipe and Collins, Karen A. and Bieryla, Allyson and Parviainen, Hannu and Belinski, Alexandr A. and Esparza-Borges, Emma and Ciardi, David R. and Clark, Catherine A. and Fukui, Akihiko and Gilbert, Emily A. and Hopp, Ulrich and Ikuta, Kai and Jenkins, Jon M. and Latham, David W. and Narita, Norio and Nielsen, Louise D. and Quinn, Samuel N. and Palle, Enric and Pippert, Jan Niklas and Polanski, Alex S. and Ries, Christoph and Schmidt, Michael and Schwarz, Richard P. and Seager, Sara and Strakhov, Ivan A. and Striegel, Stephanie and Van Eyken, Julian C. and Watanabe, Noriharu and Watkins, Cristilyn N. and Winn, Joshua N. and Ziegler, Carl and Zöller, Raphael}},
  issn         = {{0004-6361}},
  keywords     = {{Planetary systems; Planets and satellites: detection; Planets and satellites: gaseous planets; Techniques: photometric; Techniques: radial velocities}},
  language     = {{eng}},
  month        = {{02}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{TOI-5108 b and TOI 5786 b : Two transiting sub-Saturns detected and characterized with TESS, MaHPS, and SOPHIE}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/202451676}},
  doi          = {{10.1051/0004-6361/202451676}},
  volume       = {{694}},
  year         = {{2025}},
}