标题： 危险物质。 V. K型恒星的紫外线和X射线演化 显示英文标题

标题： HAZMAT. V. The Ultraviolet and X-ray Evolution of K Stars

摘要： 了解一颗行星形成和演化期间恒星的高能辐射环境对于确定该行星是否可能宜居以及能否探测到任何生物特征至关重要，因为紫外线辐射可能会严重改变或摧毁一颗行星的大气层。 目前寻找潜在宜居行星的努力主要集中在M型恒星上，但K型恒星由于活动性较低和更远更宽的宜居带（HZ），可能提供更多的宜居条件。 虽然M型恒星的活动演化已经通过光度测量和光谱测量被观测到，但对于K型恒星的紫外线演化尚未进行专门的研究。 我们展示了关于K型恒星近紫外、远紫外和X射线演化的首个综合研究。 我们使用了从10到625百万年（Myr）不同年龄的年轻移动群和星团成员，结合场星及其存档的GALEX紫外数据和ROSAT X射线数据，以确定紫外线和X射线辐射如何随时间演化。 我们发现，K型矮星宜居带行星接收到的紫外线和X射线通量比早期M型矮星宜居带行星低5到50倍，比晚期M型矮星宜居带行星低50到1000倍，这既是因为K型矮星的固有活动性降低早于M型矮星，也是因为K型矮星宜居带距离较远。 显示英文摘要

摘要： Knowing the high-energy radiation environment of a star over a planet's formation and evolutionary period is critical in determining if that planet is potentially habitable and if any biosignatures could be detected, as UV radiation can severely change or destroy a planet's atmosphere. Current efforts for finding a potentially habitable planet are focused on M stars, yet K stars may offer more habitable conditions due to decreased stellar activity and more distant and wider habitable zones (HZ). While M star activity evolution has been observed photometrically and spectroscopically, there has been no dedicated investigation of K-star UV evolution. We present the first comprehensive study of the near-UV, far-UV, and X-ray evolution of K stars. We used members of young moving groups and clusters ranging in age from 10 - 625 Myr combined with field stars and their archived GALEX UV and ROSAT X-ray data to determine how the UV and X-ray radiation evolve. We find that the UV and X-ray flux incident on a HZ planet is 5 - 50 times lower than that of HZ planets around early-M stars and 50 - 1000 times lower than those around late-M stars, due to both an intrinsic decrease in K dwarf stellar activity occurring earlier than for M dwarfs and the more distant location of the K dwarf HZ.