Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley
Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley
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DOI：
10.1051/0004-6361/202348180
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发表时间：
2024-02-06
影响因子：
6.5
通讯作者：
Zingales，T.
中科院分区：
文献类型：
--
作者：
Bonfanti，A.;Brady，M.;Zingales，T.
上下文。TOI-732是一颗M矮星，拥有两颗凌日行星，它们位于半径谷的两侧。推断这类系统的可靠人口统计数据是理解其形成和演化机制的关键。通过将可用的天基观测次数增加一倍，并增加径向速度（RV）测量次数，我们的目标是改进TOI-732 b和c的参数。我们还利用这些结果研究了具有良好特征的m矮系外行星样本的半径谷和密度谷的斜率。我们通过联合模拟地面光曲线、CHEOPS和TESS观测数据，以及从文献中获得的由MAROON-X光谱仪获得的RV时间序列，进行了全球马尔可夫链蒙特卡罗分析。利用支持向量机（SVM）方法对m矮谷的坡度进行了量化。TOI-732b是一颗超短周期行星（P= 0.76837931-0.00000042+0.0000039天），其半径rb = 1.315 -0.058+0.057R⊕，质量mb = 2.46±0.19M⊕，因此平均密度ρb= 5.8-0.8+1.0g cm-3，而外行星atP= 12.252284±0.000013天，其rc = 2.39-0.11+0.10R⊕,Mc= 8.04-0.48+0.50M⊕，因此ρc= 3.24-0.43+0.55g cm-3。即使与最近报道的值相比，这项工作也产生了过境深度和RV半振幅的不确定性，TOI-732 b和TOI-732 c的不确定性分别为~1.6和~2.4。我们对内部结构和行星在质量半径图中的位置的计算使我们将TOI-732 b归类为超级地球，TOI-732 c归类为迷你海王星。根据SVM方法，我们量化了d logP，山谷/ d logP= -0.065-0.013+0.024，比类太阳恒星更平坦。根据之前的分析，我们注意到m矮行星的半径谷密度更大，我们进一步量化密度谷的斜率为d log ρ^valley/ d logP= -0.02-0.04+0.12。与FGK恒星相比，半径谷的位置对轨道周期的依赖性较弱，这可能表明M矮星周围的形成比演化机制更强烈地塑造了半径谷。
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+0.0000039days) with a radiusRb= 1.325-0.058+0.057R⊕, a massMb= 2.46 ± 0.19M⊕, and thus a mean densityρb= 5.8-0.8+1.0g cm-3, while the outer planet atP= 12.252284 ± 0.000013 days hasRc= 2.39-0.11+0.10R⊕,Mc= 8.04-0.48+0.50M⊕, and thusρc= 3.24-0.43+0.55g 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 logRp,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 logP= -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.