HAZMAT. V. The Ultraviolet and X-ray Evolution of K Stars. (arXiv:1901.00502v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Richey_Yowell_T/0/1/0/all/0/1">Tyler Richey-Yowell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shkolnik_E/0/1/0/all/0/1">Evgenya L. Shkolnik</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schneider_A/0/1/0/all/0/1">Adam C. Schneider</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Osby_E/0/1/0/all/0/1">Ella Osby</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barman_T/0/1/0/all/0/1">Travis Barman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Meadows_V/0/1/0/all/0/1">Victoria S. Meadows</a>
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.
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.
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