학술논문
Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley ★,★★
Document Type
Author
Bonfanti, A.; Brady, M.; Wilson, T.G.; Venturini, J.; Egger, J. A.; Brandeker, A.; Sousa, S. G.; Lendl, M.; Simon, A.E.; Queloz, D.; Olofsson, G.; Adibekyan, V.; Alibert, Y.; Fossati, L.; Hooton, M.J.; Kubyshkina, D.; Luque, R.; Murgas, F.; Mustill, A. J.; Santos, N. C.; Van Grootel, V.; Alonso, R.; Asquier, J.; Bandy, T.; Bárczy, T.; Navascues, D. Barrado; Barros, S.C.C.; Baumjohann, W.; Bean, Jacob L.; Beck, M.; Beck, T.; Benz, W.; Bergomi, M.; Billot, N.; Borsato, L.; Broeg, C.; Collier Cameron, A.; Csizmadia, Szilard; Cubillos, P. E.; Davies, M. B.; Deleuil, M.; Deline, A.; Delrez, L.; Demangeon, O.; Demory, B.O.; Ehrenreich, D.; Erikson, Anders; Fortier, A.; Fridlund, Malcolm, 1952; Gandolfi, D.; Gillon, Michaël; Gudel, M.; Günther, Maximilian N.; Heitzmann, A.; Helling, Ch.; Hoyer, S.; Isaak, K.; Kasper, D.; Kiss, L. L.; Lam, K. W.F.; Laskar, J.; des Etangs, A. L.; Magrin, D.; Maxted, P.; Mordasini, C.; Nascimbeni, Valerio; Ottensamer, R.; Pagano, I.; Palle, Enric; Peter, G.; Piotto, Giampaolo P.; Pollacco, D.; Ragazzoni, R.; Rando, N.; Rauer, H.; Ribas, I.; Scandariato, Gaetano; Segransan, D.; Seifahrt, A.; Smith, A. M.S.; Stalport, M.; Stefánsson, G.; Steinberger, M.; Stürmer, J.; Szabó, G.M.; Thomas, Nicolas; Udry, S.; Villaver, E.; Walton, N. A.; Westerdorff, K.; Zingales, Tiziano
Source
Astronomy and Astrophysics. 682
Subject
Language
English
ISSN
0004-6361
1432-0746
1432-0746
Abstract
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-732 b is an ultrashort-period planet (P = 0.76837931−+000000004200000039 days) with a radius Rb = 1.325+−00057058 R☉, a mass Mb = 2.46 ± 0.19 M☉, and thus a mean density ρb = 5.8+−1008 g cm−3, while the outer planet at P = 12.252284 ± 0.000013 days has Rc = 2.39+−001011 R☉, Mc = 8.04+−005048 M☉, and thus ρc = 3.24+−005543 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 log P = −0.065+−00024013, 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 ρ̂valley/d log P = −0.02+−001204. 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.