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The recent discovery of the seven planet TRAPPIST--1 system comma including three habitable zone planets comma has opened up a new avenue for studying temperate terrrestrial planets comma with potentially habitable atmospheres. This system and others like it around the lowest-mass stars will be prime targets for both planet searches and studies to directly characterize the atmospheres of Earth-sized exoplanets. Understanding these atmospheric observations and the potential prospect of such exoplanets to develop and sustain life critically depends on the high-energy stellar radiation environment from X-ray to ultraviolent wavelengths because of the ability of this emission to drive atmospheric mass-loss comma and it.s strong influence on planetary photochemistry comma including its ability to catalyze prebiotic chemical pathways. However comma little is known about the X-ray to UV radiation field of stars at the end of the main sequence. We propose a survey of the joint X-ray and UV emission of a sample of M7-M9 dwarfs comma to provide the basis for estimating the high-energy stellar radiation environment around these stars across a range of activity levels comma and to use these spectral observations as inputs to planetary photochemsitry models. Furthermore comma these observations will probe the nature of chromospheric and coronal heating in the coolest stellar atmospheres.近期发现的TRAPPIST-1七行星系统（包含三颗宜居带（habitable zone）行星），为研究拥有潜在宜居大气的温带类地行星（terrestrial planet）开辟了全新的研究途径。该系统与其他围绕低质量恒星运行的同类系统，将成为行星搜寻以及直接表征地球大小系外行星（exoplanet）大气特征的优先观测目标。要理解此类大气观测结果，以及这类系外行星孕育并维持生命的潜在可能性，关键在于明确从X射线（X-ray）到紫外线（UV）波段的高能恒星辐射环境：这类辐射能够驱动大气质量流失，同时对行星光化学（photochemistry）过程产生强烈影响——包括催化前生物化学通路（prebiotic chemical pathways）的能力。然而，目前对于主序星演化末期恒星的X射线至紫外线辐射场仍知之甚少。我们提议对一组M7-M9型矮星（M7-M9 dwarfs）样本开展X射线与紫外线联合辐射观测，以此为基础估算不同活动强度下这类恒星周围的高能恒星辐射环境，并将这些光谱观测数据作为行星光化学模型的输入参数。此外，此类观测还将探究最冷恒星大气中色球层（chromosphere）与日冕加热（coronal heating）的本质机制。