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

Abstract
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 M_J and 0.222 ± 0.015 M_J and radii of 0.938 ± 0.025 R_J and 0.99 ± 0.22 R_J, 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.

Keywords
techniques: photometric / techniques: radial velocities / planets and satellites: detection / planets and satellites: gaseous planets / planetary systems

Astronomy & Astrophysics
Volume 684, Article Number A6, Number of pages 20
2024 April

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