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

Bonfanti, A. ; Mustill, A.J. LU orcid ; Davies, M.B. LU ; Westerdorff, K. and Zingales, T. (2024) In Astronomy and Astrophysics 682.
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... (More)
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-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. (Less)
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keywords
planets and satellites: fundamental parameters, stars: fundamental parameters, techniques: photometric, techniques: radial velocities, Landforms, Markov processes, Planets, Satellites, Time series analysis, Doublings, Evolution mechanism, Formation and evolutions, Formation mechanism, Planets and satellites: fundamental parameters, Radial velocity, Stars:fundamental parameters, Support vectors machine, Techniques: photometric, Techniques: radial velocities, Support vector machines
in
Astronomy and Astrophysics
volume
682
article number
A66
publisher
EDP Sciences
external identifiers
  • scopus:85184519282
ISSN
0004-6361
DOI
10.1051/0004-6361/202348180
language
English
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yes
id
8c10e803-f46c-4d4d-9ff1-ea31d059fbee
date added to LUP
2024-03-12 15:36:58
date last changed
2024-03-12 15:38:17
@article{8c10e803-f46c-4d4d-9ff1-ea31d059fbee,
  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-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.}},
  author       = {{Bonfanti, A. and Mustill, A.J. and Davies, M.B. and Westerdorff, K. and Zingales, T.}},
  issn         = {{0004-6361}},
  keywords     = {{planets and satellites: fundamental parameters; stars: fundamental parameters; techniques: photometric; techniques: radial velocities; Landforms; Markov processes; Planets; Satellites; Time series analysis; Doublings; Evolution mechanism; Formation and evolutions; Formation mechanism; Planets and satellites: fundamental parameters; Radial velocity; Stars:fundamental parameters; Support vectors machine; Techniques: photometric; Techniques: radial velocities; Support vector machines}},
  language     = {{eng}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley★,★★}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/202348180}},
  doi          = {{10.1051/0004-6361/202348180}},
  volume       = {{682}},
  year         = {{2024}},
}