HAbitable Zones and K-star Activity across Time
The HAZKAT program expands on the Habitable Zones and M-star Activity across Time (HAZMAT) program. 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).
Team Members: Tyler Richey-Yowell (PI), Evgenya Shkolnik, Adam Schneider, R.O. Parke Loyd, Travis Barman, and Victoria Meadows.
HAZMAT. V. The Ultraviolet and X-Ray Evolution of K Stars
We find that the UV and X-ray flux incident on an 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.
(Top Left) Habitable zone distance from the star for a K star (0.8 Msol), an early-M star (0.4 Msol), and a late-M star (0.1 Msol). The opaque regions represent the conservative habitable zones, and the translucent regions are the optimistic habitable zones. The color regions correspond to key planetary evolutionary periods outlined in Figure 18. (Top Right, Bottom Left, and Bottom Right, respectively) NUV, FUV, and X-ray median excess flux in the conservative (opaque) and optimistic (translucent) habitable zone ranges, respectively.