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Our HST and Keck observational campaigns have detected for the first time escaping atmospheres around multiple young mini-Neptunes. Photoevaporation from these planets shapes exoplanet demographics but one of the biggest sources of uncertainty in modelling the outflow is the X-ray and extreme UV spectrum of the star. Stellar EUV cannot be measured due to interstellar absorption and must be inferred from the X-ray luminosity. We propose a survey to measure the X-ray spectra of four new young active stars hosting small ( and amp amp amp lt 3.5 R_Earth) planets all of which we are targeting for helium outflow observations with Keck. As a bonus XMM.s OM will measure the MUV (virgul200 nm) flux which destroys metastable helium and is therefore critical to modelling the helium signal we observe. [truncated! Please see actual data for full text]

我们的哈勃空间望远镜（Hubble Space Telescope, HST）与凯克望远镜（Keck Telescope）观测项目首次在多颗年轻迷你海王星（mini-Neptunes）周围探测到逃逸大气层。这些行星的光致蒸发作用塑造了系外行星的种群特征，但在外流模型构建中最大的不确定性来源之一，是恒星的X射线与极紫外光谱。由于星际吸收（interstellar absorption）的存在，恒星极紫外辐射无法被直接测量，必须通过X射线光度（X-ray luminosity）进行推断。我们提议开展一项巡天观测，以测量4颗新发现的年轻活动恒星的X射线光谱，这些恒星均拥有半径小于3.5倍地球半径（R_Earth）的小型行星，且我们计划以这些行星作为凯克望远镜氦外流（helium outflow）观测的目标。作为附加产出，XMM-牛顿望远镜的光学监视器（Optical Monitor, OM）将测量会破坏亚稳态氦（metastable helium）的中紫外（Mid-Ultraviolet, MUV，约200纳米）通量，这对我们建模所观测到的氦信号至关重要。[文本已截断！请查阅完整原始文本以获取全部内容]