可变X射线通量或可解释宜居带系外行星LHS 1140b的氦逃逸变化
Variable X-ray flux may explain variable helium escape from the habitable-zone exoplanet LHS 1140b
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中文总结 AI 辅助
本研究通过XMM-Newton观测发现LHS 1140b的X射线通量存在短期变化，认为短期XUV变化或小耀斑比长期变化更可能解释其氦吸收变化，并强调同步观测的重要性。
中文摘要 AI 辅助
系外行星科学的一个核心目标是理解潜在宜居世界保持大气层的条件。这一问题对于围绕M型恒星运行的行星尤为重要，因为其宜居带行星更易于观测，但这类恒星也会发出长时间的高能辐射，可能侵蚀行星大气。对于其中一个此类世界——LHS 1140b，一颗在非活跃恒星宜居带内运行的岩石行星，在其凌越宿主恒星时观测到了随时间变化的氦吸收，这与大气逃逸相符。我们利用XMM-牛顿太空望远镜进行了X射线/紫外通量观测，以检验所观测到的氦吸收变化是否可由恒星XUV通量变化解释。在18小时的观测窗口内，我们探测到X射线通量变化，其振幅为$F_\mathrm{max}/F_\mathrm{min} = 8.5^{+9.4}_{-4.4}$。我们未探测到紫外或可见光通量的变化。积分X射线通量与2018年测得的X射线通量完全一致，表明XUV通量在多年时间尺度上保持稳定。我们发现2018年的观测对2026年观测到的变化水平不敏感。我们探索了多个能同时拟合两组数据的模型，并得出结论：短期XUV变化和/或小耀斑比长期XUV变化更可能解释氦变化。对行星凌越的近红外同步观测以及XUV通量等恒星活动指标，对于确认所观测到的氦信号变化与所观测到的X射线变化之间的联系至关重要。
英文摘要
A central goal in exoplanet science is to understand the conditions under which potentially habitable worlds retain atmospheres. This question is of special interest for worlds orbiting M stars, whose habitable-zone planets are more readily observable, but which also emit prolonged high-energy radiation that can erode planetary atmospheres. For one such world, LHS 1140b, a rocky planet orbiting in the habitable zone of an inactive star, time-variable helium absorption has been observed as the planet transited in front of its host star, consistent with atmospheric escape. We present X-ray/ultraviolet flux observations with the XMM-Newton space telescope, which serve to test whether the observed helium absorption variability can be explained by stellar XUV flux variability. We detect X-ray flux variability with an amplitude of $F_\mathrm{max}/F_\mathrm{min} = 8.5^{+9.4}_{-4.4}$ within the 18-hour observing window. We do not detect variability in the UV or visible flux. The integrated X-ray flux is fully consistent with the X-ray flux measured in 2018, suggesting stable XUV flux over years-long timescales. We find that the 2018 observation was not sensitive to the level of variability observed in 2026. We explore several models that fit both datasets and conclude that short-term XUV variability and/or small flares are more likely to explain the helium variability than long-term XUV variability. Simultaneous observations of the planet-transit in the near-infrared and stellar activity indicators like XUV flux are critical to confirm the link between the observed helium signal variability and the observed X-ray variability.
发表机构
- University of Chicago（芝加哥大学）
- Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森尼天体物理中心）
- University of Florida（佛罗里达大学）
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