TOI-1199 b and TOI-1273 b: Two new transiting hot Saturns detected and characterized with SOPHIE and TESS

Serrano Bell, J.; Díaz, R. F.; Hébrard, G.; Martioli, E.; Heidari, N.; Sousa, S.; Boisse, I.; Almenara, J. M.; Alonso-Santiago, J.; Barros, S. C. C.; Benni, P.; Bieryla, A.; Bonfils, X.; Caldwell, D. A.; Ciardi, D. R.; Collins, K. A.; Cortés-Zuleta, P.; Dalal, S.; de León, J. P.; Deleuil, M.; Delfosse, X.; Demangeon, O. D. S.; Esparza-Borges, E.; Forveille, T.; Frasca, A.; Fukui, A.; Gregorio, J.; Guerrero, N. M.; Howell, S. B.; Hoyer, S.; Ikuta, K.; Jenkins, J. M.; Kiefer, F.; Latham, D. W.; Marino, G.; Michaels, E. J.; Moutou, C.; Murgas, F.; Narita, N.; Palle, E.; Parviainen, H.; Santos, N. C.; Stassun, K. G.; Winn, J. N.
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Astronomy and Astrophysics

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We report the characterization of two planet candidates detected by the Transiting Exoplanet Survey Satellite (TESS), TOI-1199 b and TOI-1273 b, with periods of 3.7 and 4.6 days, respectively. Follow-up observations for both targets, which include several ground-based light curves, confirmed the transit events. High-precision radial velocities from the SOPHIE spectrograph revealed signals at the expected frequencies and phases of the transiting candidates and allowed mass determinations with a precision of 8.4% and 6.7% for TOI-1199 b and TOI-1273 b, respectively. The planetary and orbital parameters were derived from a joint analysis of the radial velocities and photometric data. We find that the planets have masses of 0.239 ± 0.020 MJ and 0.222 ± 0.015 MJ and radii of 0.938 ± 0.025 RJ and 0.99 ± 0.22 RJ, respectively. The grazing transit of TOI-1273 b translates to a larger uncertainty in its radius, and hence also in its bulk density, compared to TOI-1199 b. The inferred bulk densities of 0.358 ± 0.041 g cm−3 and 0.28 ± 0.11 g cm−3 are among the lowest known for exoplanets in this mass range, which, considering the brightness of the host stars (V≈11 mag), render them particularly amenable to atmospheric characterization via the transit spectroscopy technique. The better constraints on the parameters of TOI-1199 b provide a transmission spectroscopy metric of 134 ± 17, making it the better suited of the two planets for atmospheric studies.