TESS寻找年轻和成熟的系外行星（THYME）III：400 Myr Ursa Major Group中的双行星系统
TESS Hunt for Young and Maturing Exoplanets (THYME) III: a two-planet system in the 400 Myr Ursa Major Group
摘要：
系外行星可以在出生和成熟之间显著进化，因为它们的大气层，轨道和结构都是由它们的环境塑造的。年轻的行星（$<$ 1 Gyr）提供了一个探索这种演化的关键早期阶段的机会，在那里行星演化最快。然而，大多数已知的年轻行星都围绕着极其微弱的恒星运行。我们发现了两颗行星过境HD 63433（TOI 1726，TIC 130181866），一颗年轻的类太阳（$M_*=0.99\pm0.03$）恒星。通过运动学、锂丰度和旋转，我们确认HD 63433是大熊座移动群（$τ=414\pm23$ Myr）的成员。根据TESS光变曲线和更新的恒星参数，我们估算出这两颗行星的半径分别为$2.15\pm0.10R_\oplus$和$2.67\pm0.12R_\oplus$，轨道周期分别为7.11和20.55天，轨道偏心率小于0.2。利用HARPS-N速度，我们测量了内行星的Rossiter McLaughlin信号，表明轨道是倾斜的。由于主星是明亮的（V=6.9），这两颗行星都可以进行透射光谱学，径向速度测量它们的质量，并更精确地确定恒星的质量。因此，这个系统将在我们理解行星系形成后的第一个十亿年的演化过程中发挥重要作用。
英文摘要：
Exoplanets can evolve significantly between birth and maturity, as their atmospheres, orbits, and structures are shaped by their environment. Young planets ($<$1 Gyr) offer an opportunity to probe the critical early stages of this evolution, where planets evolve the fastest. However, most of the known young planets orbit prohibitively faint stars. We present the discovery of two planets transiting HD 63433 (TOI 1726, TIC 130181866), a young Sun-like ($M_*=0.99\pm0.03$) star. Through kinematics, lithium abundance, and rotation, we confirm that HD 63433 is a member of the Ursa Major moving group ($τ=414\pm23$ Myr). Based on the TESS light curve and updated stellar parameters, we estimate the planet radii are $2.15\pm0.10R_\oplus$ and $2.67\pm0.12R_\oplus$, the orbital periods are 7.11 and 20.55 days, and the orbital eccentricities are lower than about 0.2. Using HARPS-N velocities, we measure the Rossiter-McLaughlin signal of the inner planet, demonstrating that the orbit is prograde. Since the host star is bright (V=6.9), both planets are amenable to transmission spectroscopy, radial velocity measurements of their masses, and more precise determination of the stellar obliquity. This system is therefore poised to play an important role in our understanding of planetary system evolution in the first billion years after formation.
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