Characterising TOI-732 b and c: new insights on the M-dwarf radius and density valley. (arXiv:2311.12577v1 [astro-ph.EP])

Characterising TOI-732 b and c: new insights on the M-dwarf radius and density valley. (arXiv:2311.12577v1 [astro-ph.EP])
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TOI-732 is an M dwarf hosting two transiting planets, which are located on
the two opposite sides of the radius valley. 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 ($Psim0.77$ d) with a radius
$R_b=1.325_{-0.058}^{+0.057}$ $R_{oplus}$ and a mass $M_b=2.46pm0.19$
$M_{oplus}$ (mean density $rho_b=5.8_{-0.8}^{+1.0}$ g cm$^{-3}$), while the
outer planet at $Psim12.25$ d has $R_c=2.39_{-0.11}^{+0.10}$ $R_{oplus}$,
$M_c=8.04_{-0.48}^{+0.50}$ $M_{oplus}$, and thus $rho_c=3.24_{-0.43}^{+0.55}$
g cm$^{-3}$. Also considering our interior structure calculations TOI-732 b is
a super-Earth and TOI-732 c is a mini-Neptune. Following the SVM approach, we
quantified
$mathrm{d}log{R_{p,{mathrm{valley}}}}/mathrm{d}log{P}=-0.065_{-0.013}^{+0.024}$,
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
$mathrm{d}log{hat{rho}_{mathrm{valley}}}/mathrm{d}log{P}=-0.02_{-0.04}^{+0.12}$.
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.

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