The LHS 1678 System: Two Earth-sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc
The LHS 1678 System: Two Earth-sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc
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DOI：
10.3847/1538-3881/ac32e3
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发表时间：
2021-10
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影响因子：
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通讯作者：
M. Silverstein;J. Schlieder;T. Barclay;B. Hord;W. Jao;E. Vrijmoet;T. Henry;R. Cloutier;V. Ko
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作者：
M. Silverstein;J. Schlieder;T. Barclay;B. Hord;W. Jao;E. Vrijmoet;T. Henry;R. Cloutier;V. Ko
我们介绍了凌日系外行星调查卫星(TESS)发现的LHS1678(TOI-696)系外行星系统，该系统由两颗大约地球大小的凌日行星和一颗可能的天体测量棕矮星组成，在19.9pc绕着一颗明亮的M2矮星(VJ=12.5，K S=8.3)运行。TESS探测到的两颗行星在0.86d和3.69d轨道上的半径分别为0.70±0.04R⊕和0.98±0.06R⊕。这两颗行星都通过地面后续观测得到了验证和表征。高精度径向速度行星搜索器RV监测得出b和c行星的质量上限分别为0.35M⊕和1.4M⊕，质量上限为97.7%。Cerro Tololo美洲天文台/中小口径望远镜系统0.9米探测到的天体测量伴星的轨道周期为几十年，其他手段没有探测到。额外的地面观测将这颗伴星限制在高质量的棕矮星或更小的范围内。每一颗行星都有独特的兴趣；内行星的周期非常短，而外行星位于金星带。这两个目标都是利用詹姆斯·韦伯太空望远镜进行大气特征描述和通过极精确的径向速度进行质量测量的有前途的目标。在多周期TESS数据中还发现了半径为0.9±0.1R⊕的第三颗行星，该行星的轨道为4.97d，可供今后工作验证。主星与赫兹斯普龙格-罗素图较低主序列中观察到的空隙有关。这一差距与M矮星从部分对流内部到完全对流内部的转变有关，相关的恒星天体物理对系外行星演化的影响目前尚不清楚。这些系统性质的巅峰使LHS 1678成为比较系外行星科学和了解围绕低质量恒星运行的短周期小型系外行星的形成和演化的独特、引人注目的游乐场。
We present the Transiting Exoplanet Survey Satellite (TESS) discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright (V J = 12.5, K s = 8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70 ± 0.04 R ⊕ and 0.98 ± 0.06 R ⊕ in 0.86 day and 3.69 day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. High Accuracy Radial Velocity Planet Searcher RV monitoring yields 97.7 percentile mass upper limits of 0.35 M ⊕ and 1.4 M ⊕ for planets b and c, respectively. The astrometric companion detected by the Cerro Tololo Inter-American Observatory/Small and Moderate Aperture Telescope System 0.9 m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the James Webb Space Telescope and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9 ± 0.1 R ⊕ in a 4.97 day orbit is also identified in multicycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung–Russell diagram. This gap is tied to the transition from partially to fully convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars.