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arXiv 1906.08795astro-ph.EP
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寻找来自解体的岩石系外行星K2-22b的气体

Search for gas from the disintegrating rocky exoplanet K2-22b

A. R. Ridden-Harper, I. A. G. Snellen, C. U. Keller, P. Mollière

摘要:

[摘要]目的。我们在解体的岩石系外行星K2-22 b周围寻找环行钠和电离钙气体,以限制其气体损失和升华过程。方法.我们在ESO甚大望远镜上用X射线摄影仪观测了K2-22 b的4次凌日,获得了中分辨率(R $\sim$ 11400)谱的时间序列。我们的分析集中在两个钠D线(588.995 nm和589.592 nm)和Ca $^{+}$三重态(849.802 nm,854.209 nm和866.214 nm)。在行星的速度静止坐标系中搜索与行星相关的吸收,该坐标系在凌日期间从$\pm$ 66 km $^{-1}$变化。结果由于K2-22 b具有高度可变的过境深度,我们分析了各个夜晚及其平均值。通过注射信号,我们在单个夜晚达到了5个$σ$上限,分别为尾部钠和离子钙吸收的11% - 13%和1.7% - 2.0%。Night 1被它的伴星污染,所以我们考虑了有和没有Night 1的加权平均值,并引用了保守的5 $σ$限制,分别为9%和1.4%。假设它们的质量分数与地壳中的质量分数相似,这些极限对应于0.04%和35%的过境尘埃升华并被观察为吸收气体的情况。然而,这假设气体与行星共同运动。我们发现,在K2-22 b的高辐射环境中,由于辐射压力和星风的夹带,钠和离子钙可以迅速加速到100 s km/s的$^{-1}$,使它们更难被探测到。在我们的数据中没有看到这种可能广泛和蓝移信号的证据。结论.今后旨在观测环行行星气体的观测应考虑到原子和电离物质可能存在的广泛和蓝移速度场。

英文摘要:

[Abridged] Aims. We searched for circumplanetary sodium and ionized calcium gas around the disintegrating rocky exoplanet K2-22 b to constrain its gas-loss and sublimation processes. Methods. We observed four transits of K2-22 b with X-shooter on ESO's Very Large Telescope to obtain time-series of intermediate-resolution (R $\sim$ 11400) spectra. Our analysis focused on the two sodium D lines (588.995 nm and 589.592 nm) and the Ca$^{+}$ triplet (849.802 nm, 854.209 nm and 866.214 nm). Planet-related absorption is searched for in the velocity rest frame of the planet, which changes from $\pm$66 kms$^{-1}$ during the transit. Results. Since K2-22 b exhibits highly variable transit depths, we analyzed the individual nights and their average. By injecting signals we reached 5$σ$ upper-limits on the individual nights that ranged from 11% - 13% and 1.7% - 2.0% for the tail's sodium and ionized calcium absorption, respectively. Night 1 was contaminated by its companion star so we considered weighted averages with and without Night 1 and quote conservative 5$σ$ limits without Night 1 of 9% and 1.4%, respectively. Assuming their mass fractions to be similar to those in the Earth's crust, these limits correspond to scenarios in which 0.04% and 35% of the transiting dust is sublimated and observed as absorbing gas. However, this assumes the gas to be co-moving with the planet. We show that for the high irradiation environment of K2-22 b, sodium and ionized calcium could be quickly accelerated to 100s of km s$^{-1}$ due to radiation pressure and entrainment by the stellar wind, making them much more difficult to detect. No evidence for such possibly broad and blue-shifted signals are seen in our data. Conclusions. Future observations aimed at observing circumplanetary gas should take into account the possible broad and blue-shifted velocity field of atomic and ionized species.

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