TOI-732 is an M dwarf hosting two transiting planets, which are located on the two opposite sides of the radius valley. Inferring a reliable demographics for these kind of systems is key to understand their formation and evolution mechanisms. 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 aim at using the results to study the slope of both the radius valley and the density valley for a well characterised sample of M dwarf exoplanets. We performed a global MCMC analysis by jointly modelling ground-based light curves, 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. TOI-732 b is an ultra short period planet (P=0.76837931_-0.00000042_^+0.00000039^d) with a radius R_b_=1.325_-0.058_^+0.057^R_{Earth}_, a mass M_b_=2.46+/-0.19M_{Earth}_, and thus a mean density rho_b_=5.8_-0.8_^+1.0^g/cm^3^, while the outer planet at P=12.252284+/-0.000013d has R_c_=2.39_-0.11_^+0.10^R_{Earth}_, M_c_=8.04_-0.48_^+0.50^M_{Earth}_, and thus rho_c_=3.24_-0.43_^+0.55^g/cm^3^. Even with respect to the most recently reported values, this work yields to smaller uncertainties on the transit depths and on the RV semi-amplitudes up to a factor of ~1.6 and ~2.4 for TOI-732 b and c, respectively. Both our interior structure calculations and the location of the planets in the Mass-Radius diagram leads us to classify TOI-732 b as a super-Earth and TOI-732 c as a mini-Neptune. Following the SVM approach, we quantified Rslope=-0.065_-0.013_^+0.024^, which is flatter than for Sun-like stars. In line with former analyses, we noted a more filled radius valley for M-planets and we further quantified the density valley slope as Rhoslope=-0.02_-0.04_^+0.12^. Compared to FGK stars, the weaker dependence of the position of the radius valley with orbital period might indicate a heavier influence of formation relative to evolution mechanisms in shaping the radius valley around M-dwarfs.

Bonfanti, A. et al. -- TOI-732 detrended CHEOPS and TESS light curves. The Characterising Exoplanet Satellite (CHEOPS) collected 25 light curves of TOI-732 from January 8 to April 10, 2022. The Transiting Exoplanet Survey Satellite (TESS) observed the system in cycle 1 (Sector 8; from 28 February to 26 March 2019) in cycle 3 (Sector 35; from 9 February to 7 March 2021), and in cycle 5 (Sector 62; from 12 February to 10 March 2023).

Peer reviewed