Low-mass stars are currently the most promising targets for detecting and characterizing habitable planets in the solar neighborhood .
However , the ultraviolet ( UV ) radiation emitted by such stars can erode and modify planetary atmospheres over time , drastically affecting their habitability .
Thus knowledge of the UV evolution of low-mass stars is critical for interpreting the evolutionary history of any orbiting planets . [ Shkolnik & Barman ( 2014 ) ] used photometry from the Galaxy Evolution Explorer ( GALEX ) to show how UV emission evolves for early type M stars ( > 0.35 M _ { \odot } ) .
In this paper , we extend their work to include both a larger sample of low-mass stars with known ages as well as M stars with lower masses .
We find clear evidence that mid- and late-type M stars ( 0.08–0.35 M _ { \odot } ) do not follow the same UV evolutionary trend as early-Ms. Lower mass M stars retain high levels of UV activity up to field ages , with only a factor of 4 decrease on average in GALEX NUV and FUV flux density between young ( < 50 Myr ) and old ( \sim 5 Gyr ) stars , compared to a factor of 11 and 31 for early-Ms in NUV and FUV , respectively .
We also find that the FUV/NUV flux density ratio , which can affect the photochemistry of important planetary biosignatures , is mass and age-dependent for early Ms , but remains relatively constant for the mid- and late-type Ms in our sample .