Full Citation: Richey-Yowell, T., Shkolnik, E. L., Schneider, A. C., Osby, E., Barman, T., & Meadows, V. S. (2019). Hazmat. V. The Ultraviolet And X-Ray Evolution Of K Stars. The Astrophysical Journal, 872 (1), 17. https://doi.org/10.3847/1538-4357/aafa74.
Abstract: 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 (HZs). 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 to 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 an HZ planet is 550 times lower than that of HZ planets around early-M stars and 501000 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.
URL: https://doi.org/10.3847/1538-4357/aafa74