A. Bonfanti, M. Brady, T. G. Wilson, J. Venturini, J. A. Egger, A. Brandeker, S. G. Sousa, M. Lendl, A. E. Simon, D. Queloz, G. Olofsson, V. Zh. Adibekyan, Y. Alibert, L. Fossati, M. J. Hooton, D. Kubyshkina, R. Luque, F. Murgas, A. J. Mustill, N. C. Santos, V. Van Grootel, R. Alonso, J. Asquier, T. Bandy, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, W. Baumjohann, J. L. Bean, M. Beck, T. Beck, W. Benz, M. Bergomi, N. Billot, L. Borsato, C. Broeg, A. Collier Cameron, S. Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, A. Deline, L. Delrez, O. D. S. Demangeon, B.-O. Demory, D. Ehrenreich, A. Erikson, A. Fortier, M. Fridlund, D. Gandolfi, M. Gillon, M. Güdel, M. N. Günther, A. Heitzmann, C. Helling, S. Hoyer, K. G. Isaak, D. Kasper, L. L. Kiss, K. W. F. Lam, J. Laskar, A. Lecavelier Des Etangs, D. Magrin, P. F. L. Maxted, C. Mordasini, V. Nascimbeni, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, G. Scandariato, D. Ségransan, A. Seifahrt, A. M. S. Smith, M. Stalport, G. Stefánsson, M. Steinberger, J. Stürmer, G. M. Szabó, N. L. Thomas, S. Udry, E. Villaver, N. A. Walton, K. Westerdorff, T. Zingales
Abstract
Context. TOI-732 is an M dwarf hosting two transiting planets that are located on the two opposite sides of the radius valley. Inferring a reliable demographics for this type of systems is key to understanding their formation and evolution mechanisms.
Aims. By doubling the number of available space-based observations and increasing the number of radial velocity (RV) measurements, we aim at refining the parameters of TOI-732 b and c. We also use the results to study the slope of the radius valley and the density valley for a well-characterised sample of M-dwarf exoplanets.
Methods. We performed a global Markov chain Monte Carlo analysis by jointly modelling ground-based light curves and CHEOPS and TESS observations, along with RV time series both taken from the literature and obtained with the MAROON-X spectrograph. The slopes of the M-dwarf valleys were quantified via a support vector machine (SVM) procedure.
Results. TOI-732b is an ultrashort-period planet (P = 0.76837931-0.00000042+0.0000039 days) with a radius Rb = 1.325-0.058+0.057R⊕, a mass Mb = 2.46 ± 0.19 M⊕, and thus a mean density ρb = 5.8-0.8+1.0 g cm-3, while the outer planet at P = 12.252284 ± 0.000013 days has Rc = 2.39-0.11+0.10R⊕, Mc = 8.04-0.48+0.50M⊕, and thus ρc = 3.24-0.43+0.55 g cm-3. Even with respect to the most recently reported values, this work yields uncertainties on the transit depths and on the RV semi-amplitudes that are smaller up to a factor of ~1.6 and ~2.4 for TOI-732 b and c, respectively. Our calculations for the interior structure and the location of the planets in the mass-radius diagram lead us to classify TOI-732 b as a super-Earth and TOI-732 c as a mini-Neptune. Following the SVM approach, we quantified d log Rp,valley / d logP = -0.065-0.013+0.024, which is flatter than for Sun-like stars. In line with former analyses, we note that the radius valley for M-dwarf planets is more densely populated, and we further quantify the slope of the density valley as d log ρvalley / d log P = -0.02-0.04+0.12.
Conclusions. Compared to FGK stars, the weaker dependence of the position of the radius valley on the orbital period might indicate that the formation shapes the radius valley around M dwarfs more strongly than the evolution mechanisms.
Keywords
techniques: photometric / techniques: radial velocities / planets and satellites: fundamental parameters / stars: fundamental parameters
Notes
- TESS and CHEOPS detrended light curves are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/682/A66
- This article uses data from CHEOPS programme CH_PR100031.
Astronomy & Astrophysics
Volume 6832, Article Number A66, Number of pages 28
2024 February
