Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley

Journal
Date Issued
2023
Author(s)
Bonfanti, A.
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Brady, M.
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Wilson, T.G.
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Venturini, J.
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Egger, J.A.
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Brandeker, A.
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Sousa, S.G.
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Lendl, M.
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Simon, A.E.
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Queloz, D.
•
Olofsson, G.
•
Adibekyan, V.
•
Alibert, Y.
•
Fossati, L.
•
Hooton, M.J.
•
Kubyshkina, D.
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Luque, R.
•
Murgas, F.
•
Mustill, A.J.
•
Santos, N.C.
•
Van Grootel, V.
•
Alonso, R.
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Asquier, J.
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Bandy, T.
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Bárczy, T.
•
Barrado Navascues, D.
•
Barros, S.C.
•
Baumjohann, W.
•
Bean, J.
•
Beck, M.
•
Beck, T.
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Benz, W.
•
•
Billot, N.
•
•
Broeg, C.
•
Collier Cameron, A.
•
Csizmadia, Sz.
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Cubillos, P.E.
•
Davies, M.B.
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Deleuil, M.
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Deline, A.
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Delrez, L.
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Demangeon, O.D.S.
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Demory, B.-O.
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Ehrenreich, D.
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Erikson, A.
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Fortier, A.
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Fridlund, M.
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Gandolfi, D.
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Gillon, M.
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Güdel, M.
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Günther, M.N.
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Heitzmann, A.
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Helling, Ch.
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Hoyer, S.
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Isaak, K.G.
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Kasper, D.
•
Kiss, L.
•
Lam, K.W.F.
•
Laskar, J.
•
Lecavelier des Etangs, A.
•
•
Maxted, P.F.L.
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Mordasini, C.
•
•
Ottensamer, R.
•
•
Pallé, E.
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Peter, G.
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Piotto, G.
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Pollacco, D.
•
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Rando, N.
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Rauer, H.
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Ribas, I.
•
•
Ségransan, D.
•
Seifahrt, A.
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Smith, A.M.S.
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Stalport, M.
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Stefánsson, G.
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Steinberger, M.
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Stürmer, J.
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Szabó, M. Gy.
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Thomas, N.
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Udry, S.
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Villaver, E.
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Walton, N.A.
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Westerdorff, K.
•
Zingales, T.
DOI
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 ρ^valley / 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. TESS and CHEOPS detrended light curves are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://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.
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2024A&A...682A..66B
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open.access
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