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arXiv 2011.13444astro-ph.EPastro-ph.IM
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WASP-107 b的密度甚至更低：行星气体包层吸积和轨道迁移物理学的案例研究

WASP-107b's density is even lower: a case study for the physics of planetary gas envelope accretion and orbital migration

Caroline Piaulet, Björn Benneke, Ryan A. Rubenzahl, Andrew W. Howard, Eve J. Lee, Daniel Thorngren, Ruth Angus, Merrin Peterson, Joshua E. Schlieder, Michael We… 展开作者

Caroline Piaulet, Björn Benneke, Ryan A. Rubenzahl, Andrew W. Howard, Eve J. Lee, Daniel Thorngren, Ruth Angus, Merrin Peterson, Joshua E. Schlieder, Michael Werner, Laura Kreidberg, Tareq Jaouni, Ian J. M. Crossfield, David R. Ciardi, Erik A. Petigura, John Livingston, Courtney D. Dressing, Benjamin J. Fulton, Charles Beichman, Jessie L. Christiansen, Varoujan Gorjian, Kevin K. Hardegree-Ullman, Jessica Krick, Evan Sinukoff

备注：
Accepted for publication in AJ, 16 pages, 7 figures
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摘要：

WASP-107 b的质量在海王星范围内，半径与木星相当，对行星形成理论提出了挑战。同时，这颗行星的低表面重力和恒星的亮度也使其成为大气特征最有利的目标之一。在这里，我们提出了一个广泛的4年凯克/HIRES径向速度（RV）后续计划的WASP-107系统的结果，并提供了详细的研究物理管理的吸积的气体信封。我们发现WASP-107 b的质量只有1.8海王星质量（$M_b = 30.5 \pm 1.7$ $M_\oplus$）。由此产生的非常低的密度表明，WASP-107 b具有$> 85$ %的H/He包封质量分数，除非它被充分膨胀。相应的核心质量$<4.6$ $M_\oplus$在3 $σ$是显着低于传统上被认为是必要的触发大量的气体包层吸积。我们证明，这个大的气体核心质量比最合理的结果从吸积在$\gtrsim 1$ AU到低不透明度，无尘大气和随后的迁移到现在的$a_b = 0.0566 \pm 0.0017$ AU的发病。在WASP-107 b之外，我们还探测到第二颗更大质量的行星（$M_c \sin i = 0.36 \pm 0.04$ $M_{J}$），它位于一个宽偏心轨道（$e_c = 0.28 \pm 0.07$）上，这可能影响了WASP-107 b的轨道迁移和自旋轨道错位。总的来说，我们新的RV观测和包络吸积模型为WASP-107 b的有趣性质和系统的形成历史提供了重要的见解。展望未来，WASP-107 b将成为了解气体包层吸积物理学的基石。

英文摘要：

With a mass in the Neptune regime and a radius of Jupiter, WASP-107b presents a challenge to planet formation theories. Meanwhile, the planet's low surface gravity and the star's brightness also make it one of the most favorable targets for atmospheric characterization. Here, we present the results of an extensive 4-year Keck/HIRES radial-velocity (RV) follow-up program of the WASP-107 system and provide a detailed study of the physics governing the accretion of its gas envelope. We reveal that WASP-107b's mass is only 1.8 Neptune masses ($M_b = 30.5 \pm 1.7$ $M_\oplus$). The resulting extraordinarily low density suggests that WASP-107b has a H/He envelope mass fraction of $> 85$% unless it is substantially inflated. The corresponding core mass of $<4.6$ $M_\oplus$ at 3$σ$ is significantly lower than what is traditionally assumed to be necessary to trigger massive gas envelope accretion. We demonstrate that this large gas-to-core mass ratio most plausibly results from the onset of accretion at $\gtrsim 1$ AU onto a low-opacity, dust-free atmosphere and subsequent migration to the present-day $a_b = 0.0566 \pm 0.0017$ AU. Beyond WASP-107b, we also detect a second more massive planet ($M_c \sin i = 0.36 \pm 0.04$ $M_{J}$) on a wide eccentric orbit ($e_c = 0.28 \pm 0.07$) which may have influenced the orbital migration and spin-orbit misalignment of WASP-107b. Overall, our new RV observations and envelope accretion modeling provide crucial insights into the intriguing nature of WASP-107b and the system's formation history. Looking ahead, WASP-107b will be a keystone planet to understand the physics of gas envelope accretion.

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