[论文解读] THE K2-ESPRINT PROJECT I: DISCOVERY OF THE DISINTEGRATING R OCKY PLANET WITH A COMETARY HEAD AND TAIL EPIC 201637175B

Roberto Sanchis-Ojeda, S. Rappaport+29 more|arXiv (Cornell University)|Apr 16, 2015

Stellar, planetary, and galactic studies参考文献 2被引用 3

一句话总结

K2-ESPRINT项目通过多波段凌日观测发现EPIC 201637175b，一颗具有彗星状尾迹和前导尘埃尾迹的解体类地系外行星。可变的凌日深度（0–1.3%）及波长依赖的消光效应证实了尘埃导致的遮蔽，光曲线中的凸起表明存在拖后尾迹以及源自行星希尔球外洛希瓣溢出的显著前导尘埃尾迹。

ABSTRACT

We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hours: EPIC 201637175b. The highly variable transit depths, ranging from ∼0% to 1.3%, are suggestive of a planet that is disintegrating via the emission of dusty efflu ents. We characterize the host star as an M-dwarf with Teff ≃ 3800. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and ( 4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. Th e latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better st atistical precision compared with the ground-based observations. We detect a significant “bump’ just after the t ransit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context o f a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet’s Hill spher e and effectively undergo ‘Roche lobe overflow’, even though the planet’s surface is likely underfilling its R oche lobe by a factor of 2. Subject headings:planetary systems—planets and satellites: detection, atmospheres

研究动机与目标

• 调查K2场-1中一颗凌日系外行星候选体的性质，其具有极高的可变凌日深度。
• 确定该可变性是由尘埃消光还是固态天体遮挡引起。
• 利用地面和空间观测数据表征恒星并精炼凌日星历。
• 检查波长依赖的凌日深度变化，以区分尘埃与固态天体遮挡。
• 建模尘埃喷射的动力学及其通过洛希瓣溢出导致行星解体的潜在影响。

提出的方法

• 使用多台1米望远镜及大天区望远镜（GTC）进行地面凌日观测。
• 分析时间分辨率较低但统计精度更高的K2空间观测光曲线，以检测凌日异常。
• 测量波长依赖的凌日深度，以评估尘埃与固态物质引起的消光。
• 识别出在内 ingress 后和外 egress 前出现的光曲线凸起，表明存在延伸的尘埃结构。
• 建立尘埃颗粒在行星希尔球外的动力学模型，以解释前导与拖后尘埃尾迹的形成。
• 利用恒星参数（Teff ≈ 3800 K）和轨道周期（9.1457小时）约束行星系统的结构。

实验结果

研究问题

• RQ1 EPIC 201637175b 观测到的极高可变凌日深度（0–1.3%）由何原因引起？
• RQ2 观测到的可变性是由于尘埃消光还是固态天体遮挡？
• RQ3 波长依赖的凌日深度是否表明行星系统中存在尘埃？
• RQ4 光曲线在内 ingress 前和外 egress 后出现凸起的物理机制是什么？
• RQ5 观测到的尘埃结构能否通过尘埃颗粒在行星希尔球外的洛希瓣溢出机制来解释？

主要发现

• 凌日深度从约0%至1.3%不等，表明存在显著且可变的遮蔽。
• 波长依赖的凌日深度证实了恒星光的消光是由尘埃引起，而非固态天体。
• 检测到内 ingress 后的凸起以及较不显著的内 ingress 前凸起，表明存在拖后尘埃尾迹和前导尘埃尾迹。
• 前导尘埃尾迹被解释为尘埃通过洛希瓣溢出机制从行星希尔球外逃逸所致。
• 尽管行星表面的洛希瓣填充因子仅为2倍，尘埃仍能高效逃逸。
• 恒星被表征为有效温度 Teff ≈ 3800 K 的M型矮星。