Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley-猫眼课题宝

DOI：

10.1093/mnras/stab2143

发表时间：

2021-01

期刊：

Monthly Notices of the Royal Astronomical Society

影响因子：

4.8

通讯作者：

中科院分区：

物理与天体物理2区

文献类型：

作者：

V. V. Eylen-V.;N. Astudillo-Defru;X. Bonfils;J. Livingston;T. Hirano;R. Luque;K. Lam;A. B. Justesen;J. Winn;D. Gandolfi;G. Nowak;E. Pallé;S. Albrecht;F. Dai;B. C. Estrada;J. Owen;D. Foreman-Mackey;M. Fridlund;J. Korth;S. Mathur;T. Forveille;T. Mikal-Evans;H. Osborne;C. Ho;J. Almenara;É. Artigau;O. Barrag'an;S. Barros;F. Bouchy;J. Cabrera;D. Caldwell;D. Charbonneau;P. Chaturvedi;W. Cochran;S. Csizmadia;M. Damasso;X. Delfosse;J. D. Medeiros;R. D'iaz;R. Doyon;M. Esposito;G. FHur'esz;P. Figueira;I. Georgieva;E. Goffo;S. Grziwa;E. Guenther;A. Hatzes;J. Jenkins;P. Kabáth;E. Knudstrup;D. Latham;B. Lavie;C. Lovis;R. Mennickent;S. Mullally;F. Murgas;N. Narita;F. Pepe;C. Persson;S. Redfield;G. Ricker;N. Santos;S. Seager;L. Serrano;A. Smith;A. Mascareno;J. Šubjak;J. Twicken;S. Udry;R. Vanderspek;M. Z. Osorio

我们报告了L231-32（TOI-270）的精确多普勒测量结果，这是一颗附近的M矮星（d = 22 pc，M = 0.39 M，R = 0.38 R），它拥有三颗凌日行星，这些行星是最近使用凌日系外行星调查卫星（TESS）的数据发现的。这三颗行星的大小分别是地球的1.2、2.4和2.1倍，轨道周期分别为3.4、5.7和11.4天。我们获得了29个高分辨率的光谱与新委托Echelle光谱仪洛基系外行星和稳定的光谱观测（ESTERO）和58光谱使用高精度径向速度行星搜索器（HARPS）。根据这些观测，我们发现行星的质量分别为1.58 ± 0.26、6.15 ± 0.37和4.78 ± 0.43 M <$。半径和质量测量的结合表明，最里面的行星具有类似于地球的岩石成分，而外部两颗行星的密度较低。因此，内行星和外行星位于“半径谷”的相对两侧，这是半径周期图中成员相对较少的区域，这被解释为大气光蒸发的结果。我们将这些发现置于其他围绕M矮星运行的小型近距离行星的背景下，并使用支持向量机确定M矮星（Teff < 4000 K）半径谷的位置和斜率作为轨道周期的函数。我们比较了M矮半径谷的位置FGK恒星观察到的半径谷，并发现它的位置是一个很好的匹配光蒸发和核心供电的质量损失模型。最后，我们发现，M矮半径谷以下的行星的组成与剥离岩石核心一致，而大多数行星以上有一个较低的密度与存在的氢氦大气一致。

We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M⋆ = 0.39 M⊙, R⋆ = 0.38 R⊙), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 days. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M⊕, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the ‘radius valley’ — a region in the radius-period diagram with relatively few members, which has been interpreted as a consequence of atmospheric photo-evaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photo-evaporation and core-powered mass loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.

Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley

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